HELP!!!! I am stumped.....

[#1]

Posted recently on the broadband forum, regards SKYPE, and audio breakup/complete dropout.  Sussed that its not bandwidth, or the package my parents are on.... 
Tried a new webcam which worked once, then the PC suddenly started to restart eveytime the SKYPE app was used with video....
Tried the same webcam with my old Dell laptop, that has a much lower speed CPU, and all worked fine, which I now suspect narrows this down to the PC being at fault. Specs are:-
AMD athlon XP 2400+
1gb memory
New MOBO (Recently replaced due to a GPU issue)
Standard 400W PSU.
They never had any issues with SPYPE with this system up until a couple of weeks ago.
I am now thinking this is probably one of 2 things....
1..  A power supply issue, not providing enough power to the onboard USB ports.
2.. A slightly corrupt windows install.
Not sure about 1..  As they only have 3 things plugged in USB wise, a multifunction printer, thats normally off anyway. A wireless keyboard and mouse setup, and the webcam.  The latest drivers are on for everthing.
Had the system at my house for a couple of days benchmarking it, and cant get it do anything at all problem wise. For other things the system works flawlessly.  Tried a CPU burnin, in case the CPU is on its way out, to no avail, no overheating etc.  Everything else checks out fine.
Does anyone have any ideas why SKYPE audio refuses to work using a good quality webcam. The SKYPE tests all check out as well, its only when we try to use it on an actual call, it all goes pearshaped.
Does anyone know how to actually test a PSU?
Thanks

[#2]

If there was a PSU problem, then you would have noticed problems with starting the PC, as all the drives are spun up taking maximum power, and it would sit there either hung, or in a reboot loop.
The webcam power consumption is likely to be so low that I can't imagine that it is a power related problem - unless it has night vision in which case the infra-red LEDs might take quite a bit of current !.
A 400W PSU is about 100W more than your setup needs - unless you have some mega graphics card fitted, and I have had similar systems on 250W PSUs without any problems.
If the webcam was faulty then it would have taken down your laptop - but didn't.
You could check either your BIOS or Windows, to see if you can move the USB interrupt to another number, in case the USB hardware is sharing an interrupt with something else that gets upset when the webcam starts.

[#3]

Thanks.  My thought processes are along the same lines as yours.  Cant see this is a hardware error at all..  Checked the event log, and there are a few application errors, faulting the skype.exe app, with a fault address.  Also there are a couple of fault bucket errors.  Does this mean the SKYPE app is faulty.  The webcam works fine, with its own app, until we try and use SKYPE, and even then sometimes its fine, but rarely.  It even happens, when video is not being used, just a voice call using the webcam Mic.  Dont think a reinstall of Windows would do any harm, but it is a last resort,  All the USB ports report all working fine. The system also reports errors with the WINWORD.EXE app hanging as well.
All was working fine till a couple of weeks ago, and I cant seem to tie it up to anything as well.

[#4]

Just a thought as you said it started a couple of weeks ago! skype moved out of beta about that time ago
have you tried updating skype