MacBook won't wake up from sleep / boot up.

My MacBook has trouble waking up from sleep, and sometimes booting up from a normal shutdown. When I open the clamshell after I put the computer to sleep, the indicator light doesn't blink, but is lit up, and the screen is completely blank. Pressed all keys, and still it won't wake up. I've had the same problem with booting up the computer from a normal shutdown as well. I've tried holding on to the power key and doing a hard reset, but nothing seems to work. However, I can't seem to pinpoint the cause of this problem, it seems to be completely arbitrary. Sometimes, it wakes without a problem, and sometimes it just stays in "zombie" mode for .. extended periods of time.

I've also resetted the PMU, and the NVRAM as well. I'm not sure how this could affect it, but a few days ago, my CD drive broke. When I tried to boot up, the CD drive seemed to be turning to find a CD, and couldn't boot up. So I took it to the Apple guy and got the CD drive removed completely. I took the MacBook back to him with this waking up problem, and he says it's fixed, but it really isn't.

Help! I can't