whats the spec of the pc?

Firstly download(even if you did the above) this http://www.tweaknow.com/RegCleaner.html run that.
And then download this http://www.filehippo.com/download_ccleaner/ top right click on "download lastest version" run this, and basically this will delete all the obsolete internet files/cookies and stuff like that(excellent little programme, every pc should have this installed), just note that after running this all your websites/forums that you visit will require you to re-type usernames and passwords so make sure you know them all.
After that press control alt and delete and when taskmanger pops up at the bottom of the box how many processes are there?

Now click start bar then click RUN, then in this box type MSCONFIG, a box will load up, click on startup tab, and tell me how many box's have little ticks in them?

Tell me all this info and i can help you some more