2009 Macbook boots slowly, crashes a ton, but only while running OS X.

I have a 2009 white Macbook running Snow Leopard. Lately, it takes around ten minutes to boot up, and once it does I get the spinning wheel constantly and sometimes the whole OS would crash, forcing me to repeat the whole long process. Also, the fans are constantly running loudly, so it seems the system is stressed somehow. I'm run hard drive and RAM analyses and found nothing wrong with either. I tried reinstalling the OS and also restoring from Time Machine. I also reset the PRAM. Nothing worked.

I installed both Linux Mint and Windows XP to my macbook and both work flawlessly except that every now and then they hang for a second or two similarly to how OS X gets the spinning ball. But they never completely crash and they're both far more usable.

I have no idea what is wrong with my computer.

Possibly a bad or failing hard drive. The only real effective test on the hard drive is to use the S.M.A.R.T. utility. You can download it from here.

Just tried that app and it said everything was working fine. Also, would a bad hard drive affect the Mac OS X Install Disc, because that also boots remarkably slowly?

If the S.M.A.R.T. reporter says the hard drive is OK, it probably is. Booting from the DVD is normally very slow so I think we can overlook that.

I suggest reinstalling Snow Leopard. Boot with the DVD, erase the drive (not the Windows partition) and reinstall. Be sure to backup all your data first before erasing the drive.