Urgent! Won't Boot. No options left? What is wrong?

Thanks for looking at this. I'm at the end of my rope.
My MacBook was working fine the other night, but I left it on and unplugged during dinner. There should have been plenty of life left in the battery, but the screen was blank. I plugged it in and try to wake it up, but it wouldn't. I hit the power button to restart, but it wouldn't boot. I couldn't get past the grey screen with the spinning wheel. I tried everything, including zapping the PRAM and resetting the power manager.
Nothing.
I had been meaning to upgrade to Leopard, so I did. That worked. I was at least able to boot, but then other weird things started happening. For one, everything worked really slowly, and for another a lot of the Mac applications wouldn't work or function properly. Safari kept crashing, and iTunes wouldn't start at all. I couldn't even download the software through Safari for a reinstall, so I brought the zip files over from a memory stick and reinstalled them that way. It worked, but then my Microsoft Office applications went belly up.
I performed an extended hardware test using the original installation disks that shipped with the computer. It found nothing wrong, so I ordered Office 2008, and installed that. Now I can't boot again! It gets past the grey screen with the spinning wheel, but now all I get is a blue screen with a cursor that I can move. Maybe I should have quit when I was behind, but what the heck is going on? I'm going to take it to a Genius Bar and have them fix it, but does anyone have any clues as to what this is about?

Thanks!

craddock,

Can't give you a straight-up answer, but it could be the memory or something wrong with the power supply transfer to the motherboard, could even be a bad motherboard... So I think a hardware problem. How long have you had the Mac? Sounds like maybe a while. Are you in warranty or do you have Apple Care? If so, let Apple take a look at it. Otherwise, Genius bar, whatever that is...

Good luck, Noel

Reinstall leopard but do an "archive and install" instead of upgrade.

Everything tested out fine in the extended hardware test that I ran. I also installed Leopard through "archive and install" the first time as I was unable to boot up and do the simple upgrade.
It's under warranty until September, so it looks like it's going back to Apple.