InsideTech

Can you be a little more specifc about the "weird things" it is doing?

First, boot in safe mode and have your antivirus run a full system scan.  (If you did this already, do it again anyway.)

How did you re-install the OS?  Did you run a system restore from a disk partition?  Did you actually take the OS off of the drive and re-install?  If you did a system recovery, it is possible that the partition with the restore data was corrupted, infect, etc., and that could explain your problems.  If you actually did a fresh install, you could be having issues related to other aspects of the system.

Running a scan in safe mode allows your virus scanner to run a bit better and a bit faster.  There won't be any start-up programs running, and most of the clutter that runs in the background won't be there to interfere.

There are a lot of things it could be.  It could be a memory resident virus, which means you aren't getting rid of it with your virus scans, and it is still there even after the re-install.  It could also be your hard drive, your RAM, or your processor even.  All of these can cause at least one of the problems you listed having.  My first guess would be a memory resident virus though.  I'd run a virus scan, and see what you find.  If you find something, try to determine if it is the same thing you were finding before the re-install.  If it is, it is more than likely memory resident.  If that is the case, clean the virus, and do not shut down your computer.  If you shut down your computer, the virus will still be in memory, and it will be written to your hard drive again.  Instead, unplug the computer from the back.  That will cause Windows to not be able to write to the hard drive before it shuts down.  Everything loaded into memory that isn't saved to the hard drive will be lost, and, if you cleaned the virus, that will include it.  Hope this helps.