PSP Fix Power

I have bought two PSP's on ebay that had broken screens and I have fixed them both up. There are some hlepful guides online showing you how to replace the screen. The screens are much more expensive than a power button though and there are also many PSP's on ebay that just won't power on. I have searched online and cannot seem to find a guide for fixing a PSP that will not power on. Could anyone direct me to a website where I could find one or has anybody done this themselves? Was it easy? Was it harder than replacing the screen? Any help would be appreciated.

Do we get a cut of your profits? ;)

Hahaha, I wasn't going to sell the PSP that I fix, probably not.