Help! Black screen after waking MacBook from sleep!

Hello,

I have a late 2006 white MacBook, which has been working fine until a few days ago when I noticed that whenever I try to wake my computer from sleep, the screen comes on for a second and then instantly blacks out. I press the keys on the keyboard, put my hand on the trackpad, but to no avail. The screen doesn't come back on and my only recourse is to hold down the power button and turn off the machine.

I'm worried there is something wrong with my MacBook.

Any insights would be greatly appreciated.

Hmm....oddly this has just stopped happening. It seems to be an on and off problem, but a problem nonetheless.

Well, now it's happening again and even worse, when I restart my computer the screen turns black after the Apple logo pops up and does nothing. I have to hold down the power button, shut off, turn back on multiple times before I can finally get through to a regular startup.

Any idea why this is happening?

I'm going to the Genius Bar tomorrow, but my Apple Care is expired now and I don't know if they will be able to help me without a hefty fee.