If you replace that box, build your own and get something better than a HP/Compaq...
Boot to safe mode and open MSCONFIG from the run dialogue, and uncheck averything you're the least bit suspicious of. You have been loaded with spyware and adware, and need to remove the same from your system. If you really want to give it the heave ho and are aware of the assorted spyware IDs, search your registry (with REGEDIT) for them and strip them out of the registry, then look for their folders and delete those.
When you restart and the machine comes back up near normal and you can connect to the Internet, download AdAware, SpyBotS&D, SpySweeper, and HijackThis and use them to kill off any remaining spyware on your system.
Also make sure your virus killer utility is updated and running.