Black screen at beginning of boot up ?

So recently my hard drive in my mac book self-destructed, but I replaced it with a fujitsu hd, then realized that my optical drive had gone to crap and wouldn't read the restore disks, so I bought a refurbished one and installed it. Everything has been working fine for a few days, but today when I booted up my computer it went to a black screen and the little glowy blue light started up like the computer was asleep. That lasted for a minute then the gray screen came up like normal. When I shut it down and rebooted it later it did the same thing. Anyone know what could be causing this or what I need to do to fix it?

Any leads appreciated.

Michael