That sounds like an infection typical of what the file siszyd32.exe downloads. There's plenty of other malware that can cause that sort of misbehaviour, but the one mentioned is spreading fairly steadily at this time.
(Others include Sality, Alureon, and Vitro.)
Try
MBAM (you may have to rename both the installer and the main exe after installation to get it to run - recommended) and if you can run it, select everything found (update it and do a quick scan only) and select "remove selected" (which quarantines.)
Let us know the file names and paths of anything found.