To start a process of troubleshooting; do you have an osx cd? Or maybe an external firewire dvd drive?
If so, try , if you have the osx cd, to boot from the cd by restarting your computer(cd inserted) while holding down the "C" key. Once booted run Disk Utiliy.
If you have both FW dvd and osx cd, boot from the FW drive and restart while holding down the option key, and choose the FW drive when the possible startup icons show up. From there you can run Disk Utility to see if you have a hardware/software problem.
If this is new, I assume you don't have much data on it? It might be better to wipe the HD and reinstall osx, the problem is likely to disapear with little time spent troubleshooting.
There are also a number of utility programs that are bootable like DiskWarrior and my favorite Prosofts Drive Genius, these are very valuable to have on hand, along with an external DVD drive.
Starting a process of troubleshooting, this way or another, wil make figuring out your problems much easier.