Back up all your personal files - documents, folders, music and so on to cd, dvd, flash drives or an external hard drive first as everything will be lost.
Print off your passwords for future reference, I also find it useful to print off the list of programs in my add/remove programs so that I know then names of the programs I want to download.
It is an easy process to restore your pc to factory settings - as it was when you bought it but you need to prepare as I've explained, and be prepared to spend time reinstalling your programs and so on.
Before doing it, think about cleaning your computer inside and out. Remove programs you don't use, if you have lots of music, pictures and videos on the hard drive think about moving them.
Run antitrojan and antispyware software to make sure you have no nasties - these are free and good:
http://www.emsisoft.com/en/software/download/ (the third in the list)
http://www.filehippo.com/download_ad-aware/
Download and run CCleaner to get rid of unnecessary junk that you don't know about:
http://www.filehippo.com/download_ccleaner/
Make sure the fans aren't clogged with dust - this will cause your pc to overheat and crash.
As it is a laptop, make sure it is on a firm surface when you use it - putting it on your lap, on the duvet or other soft surface will stop the air getting in to keep it cool