Yes i know my PC sucks anywho,
the 2 main problem of a laggy PC are Trapped files and virus's which can easily be fixed.
Firstly you want to download CCleaner this gets rid of all the trapped crap in your PC.
Here's the link.
Download it and then run it, you want to run it from time to time so it keeps your PC clean.
Now you want Antivirus Software i recommend AVG free its what i use and its sweet.
Download that and run it, also you may want to uninstall your other Antivirus software as having too many makes your PC laggy.
Again you want to run this from time to time, like once a week unlike CCleaner which you should run every 2 days or so.
and that is basically it, very simple but makes a big difference :)
I hope this Helped you, let me know in the comments.
If you have any other Tips, let me know, again in the comments :)- CerialGuy.
EDIT - Also 'athanasian echo' mentioned about defragging your computer which helps as well :) simply go to 'my computer - right click the drive you want to defrag :ie C drive. - properties - tools tab . Defragmentation. should do this about maybe once every 2 weeks or so. Cheers for the Comment 'athanasian echo' :)
Google defraggler, this program is a beast for defragging.