Sounds to me like you have Spyware and adware slowing the CPU and Virtual Memory usage on your system. They rob is along with trojans.
Trojans-Well these guys are weird. Easc one is different. The ones that I have had have Downloaded numerous odd files. They also have odd names.
Freeing up Hard-Drive Space has no effect what so ever in your system running slow. It can help speed up the boot process, but not other usages such as gaming. Only time that it can is when the recycle bin is full. That stuff is on the RAM.