If you can't solve your problems then desperate measures should get your laptop running at full speed and properly.
If you don't know how to do any of these steps, ask before you start.
Clean the fan.
Back up all your files, music, photos, videos (you should be doing this any way).
Restore laptop to factory settings. There will be a manual on your hard drive (Start - all programs) probably under 'emachines'.
This will put your laptop to the state it was when you bought it, so be prepared to spend several hours updating Windows and other pre-installed software, and reinstalling your own software and personal files.
I do this every three years at least with all my pcs and it really does give them a new lease of life.
Before doing anything I print off screenshots of all my programs, settings, bookmarks (favourites) etc for my own reference.