Info:
I was receiving BSoDs after start-up (sometimes after few minutes of normal use). So I went to the appropriate forum and started debugging. The problem is that now my computer runs really slow and Task Manager shows that I'm using 100% CPU.

Why would this be? it was not running slow before I started debugging.

The only alterations I've made have been:

to reinstall my Wireless USB Adapter, which seems to be causing a BSoD when connected to a network (but that being dealt with elsewhere)

set my cd-drive to 1st bootable in BIOS

download, extract, burn memtest to disc and attempt to run (still have not got memtest to work)

download/install HD Tune

download/install HD Diagnostic Tool

any ideas will be appreciated.

You know how to start up task manager, go to the processes list and check which one or ones is eating all your CPU.

You could have malware, though it doesn't seem exclusively like a malware problem.

read the "How to speed up windows" guide in the guides forum.