The easy way is to use the CD/DVDs that came with your computer and redo the computer. I am surprised HP did not suggest that. Be sure to back up to a CD/DVD all of the files you want to keep.
The hard way would be to try and find the viruses and remove them. It sounds like a virus problem but with all of the rundll errors it sounds like some of the drivers may be damaged too. You might use some of the free antivirus programs (Avast, AVG) to find and remove the viruses.