I think I have some kind of virus....Help!

Hi all, new to this so bare with me. Think I picked up a virus from a website. If I explain what my computer is doing then maybe someone could chuck a bit of help this way.

I have windows xp. I cant get on the internet, i ran avast and it scans partly through then seems to crash or will get an error message. cant run any other program…e.g spybot get the same result. tried restoring my comp to an earlier date but wont let me. tried putting a different antivirus on cd then running it on my comp but same affect. now comp likes to reboot continuously however i can get into safemode but nothing seems to work in there either. getting numerous error messages such as “application layer gateway service encountered a problem and needed to close” “services exe.application error, failed to initialize properly click to terminate” “Isass.exe entry point not found, the procedure entry point NtSevEvent could not be located in the dynamic link library ntdll.dll” I havent a clue what any of that means.

Would appreciate any help and advice
thanks

Have you tried avast boot scan?

Boot time Avast Antivirus Scanning
http://www.digitalred.com/avast-boot-time.php

just tried but now I cant start avast at all now, does the memory test then nothing. I just disabled the automatic reboot of windows to try and get on normally and got a load more error messages "the logon user interface DLL msgina.dll failed to load, contact administrator or restore original dll. it seems each time i start up windows i get a new error message saying something has failed to load.

Are you using Transformation Packs?