HTTP 400 Bad Request

Really stumped for an answer on this so just plucking at straws.

Looking at a PC for a friends kid (~15 male who has installed the unusual stuff 15 males have installed - LimeWire, tons of toolbars and other questionable progs) on a Vista PC.

All 5 other PCs in the house are fine except this one.

He's constantly getting HTTP 400 Bad Request and HTTP 500 Internal Server Error messages for the last 6 weeks or so. Problem occurs with one website today, tomorrow it's fine, but another website is "broken". One day it's loads of websites, another it's a handfull.....

Updated him to 3.0.684 on the PC and removed loads of crap but still the issue remains. I'm going to try to remove NOD32 to see if it's that but is it possible there is a setting that might have been "adjusted" that could cause the problem?

Question - When you go into the Advanced Settings in NOD32 does the Default button just reset the branch your are currently on - i.e. Web Access Protection, Email Protection, Tools etc or will it do the whole tree?

 

Tried a winsock reset?

 

I did but i'll try another one.....