Frustrating Crashes - Please Help

[#1]

Suddenly, at the weekend, I started experiencing Data Execution Prevention (DEP) errors when attempting to load some files from within Windows Explorer, particularly video files.

I went to System - Perforance Options and set a DEP exception for Windows Explorer.
Since then double clicking or even dragging a file (particularly but not always video) to play causes WE to crash:
Windows Explorer has encountered a problem and needs to close. Etc. If WMP was started the that, too, crashes with the same error.
Just before this started I was having some hardware problems with discs not being recognised so I opened the case and made sure all connectors were firmly seated as were as cards, etc. but the problem persisted.
I decided to reinstall XP and start again. Even before I have re-installed all apps it's happening again.
My system is as follows:
AMD Athlon 64 x2 Dual Core 6400+
3GB RAM
6 x Internal HDD (2 SATA, 4 PATA) ATA 133 IDE Card (All Drives with their own fans)
2xDVD rewriters
600Watt Power Supply
1x Ext HDD PATA Drive (added Saturday)
I have just added the external USB PATA drive. It's an internal drive within a casing with it's own power supply direct from the mains.
XP Home with SP 2
Does anyone have any clue why this is happening and what steps I can take to eradicate it.
Cheers

Edit : I have tried with the pwer off to the External drive and still the same thing happens
Edit 2: On boot up, just before the welcome screen I get a single click noise from inside the case with a second shortly after. All drive are reasobly new with the boot drive (Western Digital 80GB) less than 5 months old.
I have AVG Free with Spybot, Adaware and ZoneAlarm. All installed before the 'net was connected so doubt if it is anything from that direction.

[#2]

among this lot:
http://www.pclinuxos.com/forum/index.php?topic=39325.0
may be the very utility disk you need.  some will have memtest86+ on them and you should first run that to determine if a ram module is failing.
one of those utility disks has anti-virus you can use to scan the hard drive.  some utilities will also scan the boot sector.
windows (haven't used in long time so recall imperfect)
if you have a bootable windows floppy/cd, run chkdsk /f and it will probably tell you it can't, but offer to schedule the run on next boot.
use the manufacturer's hard drive test utility to run checks on the hard drive for faults.
you reseated cables.  did you reseat pci cards/memory modules, etc.?  did you also examine for dust and fluff?

[#3]

Hi and thanks for the above.
I've run full diagnostics on my Boot drive with no errors or problems found.
The three gig of ram was made up of 2 matching  gigs and a third previously installed on another machine. I took the non-matching one out.
I then did another clean install of XP (completely reformatting the drive as I did). I then added the updates and progranms one at a time testing for the errors I got previously and all seemed ok for around 6 hours. Then, suddenly, it started happening again. This was just after I installed SP1 for Office 2007.
I did a restore to just before I installed Office SP1 and, after the rebbot, found the DEP errors remained.
I am at a total loss here. It seems as though disc access in Windows Explorer is slower than it used to be. And there seems to be no rhyme or reason to the clashes but definitely when I try to play a media file - especially when WMP is envoked.
Does anyone have any further ideas?
Edit : If I leave the DEP error window open Windows Explorer doesn't close. The message in the DEP window is:

Quote

Name : Windows Explorer Publisher: Microsoft Corporation.

After a while of further WE use I get an 'Explorer.EXE - Application' error box with the following message:

Quote

The instruction at @0x00000000" referenced memory at "0x00000000". The memory could not be "written". Click on OK to terminate the program Click on CANCEL to debug the program

Either option and WE closes and the desktop display is refreshed!

[#4]

As a first quick and dirty solution - turn off DEP
http://www.tech-recipes.com/windows_tips566.html

[#5]

I have already tried that with WE as the exception and I still got crashes but without the DEP error box. Just another error box informinhg me WE must terminate
Thanks anyway.
Edit: Should have mentioned that WE was already in the exception box (On it's own), I just selected (ticked) it .

[#6]

It is a long shot but your power supply may be playing up.
The reason for asking is that you have a very big system with potentially a very high 12 amp draw and it may just be starting to play up.
You didn't advise which graphics card you have but that also can have a large 12 volt draw. If you run your system through this calculator http://extreme.outervision.com/PSUEngine and add a factor for capacitor ageing (say 30%) I think you will find that your present power supply may be struggling.
From memory most of the power demand of the following components comes from the 12 v rail.
CPU, Graphics Card, Disk Drives, DVD Drives.

[#7]

Power supply, Motherboard and graphhics are all less than 6 months old.
Strange thing happened earlier when the entire PC froze. I Pressed the rest button but the PC just refuced to start up. It got as far as the motherboards title screen offering me to oportunity to Press Del, F12, etc and no further. Opened the case and the CPU fan was still on.
I powered down, unplugged the power cord then reconnected and powered up. Same thing again. Left it for around 15 minutes then notice the windows welcome screen. But not POST screem, etc. before hand that. Also, the external PATA had not been recognised. I had to power that down and on again before it got recognised. Still the crashed persist.
Entered all my details into the link you gave and it suggested 502W!
P.S> I still get the odd click that sounds like it is eminating from a HDD. But all drives have checked out OK

[#8]

A an update in the hope someone can offer a solution.
I have taken the PC to be thoroughly tested by my local dealer. One SATA drive was found to be faulty and was causing all the bootp issues (although it wasn't the boot drive) but it was thi drive that was clicking.
Memory test with all 3 gigs installed showed no problems.
I clean re-installation of XP - again and all seemed well. I had only installed the motherboard drivers, ATA divers, Microsoft updates (but not SP3) including Internet Explorer 7 and WMP 11 all of which have previously worked with no issues.
I had installed Zone Alarm and AVG Antiviris before activating the internet connection then immidiately performed the necessary updates.
I then installed an audio codec.
Then it started happening again. Occasionally Windows Explorer would take a little longer to open a folder. Then trying to view a video media file would casue the above crashes again. Sometimes I would also get a message from Dr Watson.
I have done a complete virus scan on all drive along with Spybot and adawre and no problems reported.
I am at a loss but getting ever more frusrtrated at this.

[#9]

Have you done a system restore back to before you installed the audio codec to see if that was the cause?
What codec was it?

[#10]

Thanks for your reply. I've been out all afternoon so only just read it now.
The codec file was 'ffdshow-20041003'.
Basically an AVI played OK in VLC player but no audio when played in WMP. This was after I had re-installd XP due to upgrading to a dual-core CPU. As I preferred WMP and couldn't remember which codec I needed I selected this one and it worked.
I shall try uninstalling it and seeing if that helps.
Cheers

[#11]

Nearly 24 hours since I uninstalled the above codec pack and no crashes. I have done my best to invoke one by playing as many of the media files that caused the previous crashes plus set folders to Thumbnail view but all seems OK.