Slow Start-Up

I'm not sure if you can post problems here, but worth a try. While I was playing Portal I got a strange blue screen so I shut down my computer. As I turn it back on it starts up very slow and freezes at the start up windows screen with the glowing windows logo. If I leave it like that for a few min it finally starts up. I can play high end games like MW2 and AoC for hours with no problems but I still have a slow start-up...any ideas why?