Changing speed when first connecting

[#1]

When i first connect on to the internet though my modem it disconnects three times first its at 800kbps then re-connects at about 500kbps then settles down at 160.0kbps which is slow and wont even stream video's without buffering all the time.
I have tried new filters etc but to no avail and was just wondering if its at my end with it happening everytime i connect to the internet.

[#2]

There are so many potential causes....
The first one to investigate and correct is your phone wiring, please can you describe it.
Also, the downstream attenuation (and noise margin - SNRM) on your line is very useful to know - your router shows that in its stats.

[#3]

@tonka
What type of modem are you using?
Is it a router or is it a USB modem?  If it's a USB modem you may not be able to get the line stats that HPsauce is asking for. This page may help.
As he said though, check that your phone wiring is correct.  You should have a microfilter in every socket that you have something plugged into - that includes your Sky box, if you have one. 

[#4]

Cheers for reply guys,the modem is a standard modem supplied by plus net although its not brand new one just says adsl usb on box no name,my phone line is run though a extension but that is virtually brand new and i know my speed will be reduced using this but had much faster speeds before just dropped recently.

[#5]

You'll need to do the "standard" checks!!
You'll need to start by connecting the modem via a filter to the test socket exposed when you remove the lower half of your master socket. 
If things improve when you do that the fault is likely to be with your wiring or phones.
If you can't remove the bottom half of your master socket, just plug into the socket with all your phones/extensions etc. unplugged.
Have a look at this PlusNet guide: "My Broadband Doesn't Work".  It explains what you need to do.

[#6]

Done all them checks first thing i did before posting so didnt waste anyones time,after connecting early this morning it seems fine at 672.0 kbps it seems to do it at busy times of day.