Im posting this for my girlfriends brother (doesnt know @!#$ about cars). He has a 99 sunfire and while having it down at college it started giving him problems so he brought it home. Well now that its at home....it wont start. (this has happened before). The last time it happened he took it to a shop and has them replace the battery. They also replace the ignition and ignition switch. This fixed the problem for about 2 weeks and now it wont start again. Any ideas on what the problem could be?

What exactly is it doing? Is it cranking but not starting? Is it not cranking at all? Clicking but not cranking? If the latter two, check the starter wires for corrosion, poor connection. It cold also be a faulty/dying starter motor.

Yeah need a bit more info

ill find out tonight and let you know.