PC help reqd please. Slow responding computer.

I'm getting rather pissed off with the bloody awful slow response from my pc, when typing anything I can finish a word before it appears on the screen, dragging the scroll bar down the side of a screen is virtually non responsive.
Now I know that if the pc has been clobbered by trojans and other nasties then this can affect the speed things happen on screen, but do any of you have any suggestions how to cure it.
What's the best programme to run to check out the pc's performance?

 

Try

http://www.pcpitstop.com/

Tatts and i use it quite often it'll check and advise,

 

or try defragmenting it. however it takes a while.

 

Do you have a wireless keyboard and mouse? If so then maybe a battery replacement is in order