They can pretty quickly diagnose things. The fix with your existing install may well be easy for them once they know the issue. If not, they can do the reinstall. We had it done once and, at least in our case, didn't cost us any data or apps.

Which, of course, won't work as expected, since you need it to happen.

If you can create an SD card or bootable external drive, you might be able to sort things out. Sounds like a kernel extension issue. Or, like he said, take it to the Genius bar. I personally avoid them, because I know way more than they do (sad truth, they generally just follow the script) but if you aren't handy with single-user mode, fsck, and kernel extension management you may be better off that way.

I just had my macbook upgraded to Snow Leopard as I was running 10.5.8 and it was long past its prime. The shop didn't have discs for photoshop or anything and all the 3rd party apps are all still there. I know they do perform a backup first but I don't know if the apps just stay there during the upgrade, or they reinstall them from the backup.

A reinstall of Snow Leopard failed. Booting into safe mode has had some glitches and self-powered speakers that I had plugged into the iMac were occassionally distorted yet now, plugged into another source they seem fine. I am thinking this is a hardware issue, possibly the GPU or graphics card. I bought another 24 inch iMac (for $250) and am waiting for that. I will load that one and then I can take more aggressive steps to see if I can get the older one running again.

I can live without PhotoShop for a while but I really miss the mac.