Virus or what?

Nod32 2.7 fully updated, Vista Ultimate.

It started yesterday.
After starting the PC, and entering my password on the logon screen, the desktop appeared but the cursor stayed as an hourglass and the hd was nonstop working. I could not do anything, not even open task manager. So the only solution was the reset button. After that, the pc started normal.
That happen every time I switched the PC on, since yesterday.
Today, I could not start any program which need admin approval. Just nothing appeared if double clicked, even control panel applications not.
So I restarted in save mode and was able to open the services.
There I saw a lot of entries with names like 2FF3Ab or FNOP, EIO and so on, without description, which are all pointing to executable files in side the temp folder.
I deleted the services from the registry (after I changed the owner to me, they all have been owned by SYSTEM), restarted and the PC works fine now.

My question is now, WHAT could that have been and WHY did nod32 not prevent this?

I could not submit any exe, because I delete the temp folder short before I noticed the problems, so there are no exe inside anymore...

UAC did not popup, Nod32 did not popup, but something installed itself as a system service, multiple times...

 

Anybody ever had this or know for what I shall look in the internet for research?