Computer hangs when starting up sometimes

Hello,

I'm pretty sure I have a hardware problem but was looking for some advice. My computer when starting up seems to hang when loading windows (at various points sometimes when the XP screen is up, sometimes it makes it to the desktop and hangs there). This happens most often when the computer is left not running for a couple of hours and I turn it on. After the computer makes it through loading I never have a problem running any other kind of software and it doesn't freeze up on me. This used to cause a BSOD at the start up screen but I haven't gotten one of those in quite awhile (computer just hangs up now). What do you think I should start with?

Thanks in advance!