richtx64 virus

hi guys
3 days ago my computer (winxp pro sp2) started to play sounds/music/voices few secondes after windows startup and without opening anything, any browser.
i noticed in the task manager 2 instances of iexplore.exe running without any visible window on desktop, each time i stop iexplore.exe in task manager it starts again few seconds later 2 instances just like at startup.
there was 2 unknown .exe running : richtx64.exe and wscsvc32.exe, i crashed them and looked for those names on google where i saw they where listed as malware/virus, then i deleted them manually in C:\Documents and Settings\Administrateur\Local Settings\Temp where they were located.

i noticed too that avast doesnt start anymore on windows boot, and ashserv.exe cant be launched manually aswell.
after.
on computer reboot, iexplorer.exe keeps launching invisible with audio sounds playing just like before, then i dig more on google about richtx64 and cant find a real answer.
i used Hijackthis to scan pc, and the richtx64.exe was listed, i checked it to be fixed.
then i started another set of scans with avast (last update) on all my C:/ hard drive, nothing has been found, i used Malwarebytes’ Anti-Malware too that found only minor cookies infections, but nothing about richtx64.

i started winxp in safe mode and launched scans again, nothing…
i notice that in the same dir where i found richtx64.exe C:\Documents and Settings\Administrateur\Local Settings\Temp are created on boot some files :
test.reg (that appears on each reboot after deleting)
some temp files with that kind of names :BCG8A.tmp , ypt2FC.tmp

i fixed the iexplore.exe launching on startup by renaming the exe file and making it “read only”
i tried to uninstall re install avast, but it still doesnt start anymore.

NEED HELP !!!

Are you getting “security center alert” popups as well?

yes the first time i have been booting after beeing infected i guess, the security center was pointing out that i didnt have any antivirus active as avast doesnt start anymore.

Windows XP Service Pack 3 has been available for over a year and provides many Critical Updates plus performance improvements.

You need to start Internet Explorer then go to Tools then Windows Update and download all of the available updates.

Go to Control Panel then Automatic Updates then select Automatic (recommended) or at least Notify me but don’t automatically download or install them.

Go to Secunia Online Software Inspector then run it to see what other applications are vulnerable:
http://secunia.com/vulnerability_scanning/online