Virus or trojan help

hello..
I am infected with a virus or a trojan that will not allow me to execute and 
install any antivirus software or even install any windows updates offline 
or online... It simply deletes certain exe files when extracted to the hard 
disk.. and the software installation gives an error saying it cannot find 
the file...

I tried booting in safemode from xp and extract the files manualy but the 
antivirus wont install because its safemode so I boot xp normaly and browse 
to the extraction directory only to find right in front of my eyes the exe 
being deleted by the unknown virus.. tried different antivirus and they all 
wont install... but other software that is not an antivirus will install... 
I tried using an online scanner from bitdefender but it did not detect any..
I tried closing all running process in task manager and services running 
still no avail..

anyone knows what virus or trojan that acts like this..can anyone please 
inform me of its name so I may come to the right way of tracking a 
solution..

thanks... 




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