Boots in safe mode but hangs at blue screen otherwise

Thanks, Mayer. Actually, I had already done that, it didn't make a difference. Furthermore, after getting it to boot in single user mode, I ran fsck -fy and it did some repairs. I was suspicious that the disk might be going bad, so I installed a new hard disk and reinstalled OS X. No difference, i.e., it still hangs at the blue screen unless I use Safe Mode. What should I check next?

Booting from the install disk and holding D just brings me to the blue screen, it didn't appear to do anything. I powered down the MBP, inserted the DVD, then pressed the pwer switch and held down the Option key. When it showed the choice of hard drive or DVD drive, I selected the DVD drive. I held the D key down from the moment I clicked on that until a minute or so after the pinwheel started. My install disk is the Mac OS X Leopard install disk from a box set. Are those diagnostics on that disk?

So, today a Mac shop told me over the phone that based on the symptoms and various things I'd tried, it was the logic board ($600 repair). At least that was more info than the Apple Genius Bar, which told me my MBP was so old that Apple no longer supports it. If anyone has any other ideas of possible causes and cheaper fixes, they would be much appreciated!