After you remove the keyboard/top case, you should be okay to do that - I've done it with different keyboards myself. After that I would take a toothbrush, and firmly but gently, brush around (and under) all of the keys with it, then rinse it again. Shake it to remove the excess water.
The tricky part is waiting for it to completely dry before reattaching it. I've always found a gas oven (radiators also) perfect for this kind of thing - don't even have to turn it usually - just lay the pieces on a towel on the racks. If you have to turn it on, then wait til it warms up, then give it a few moments to "chill", then put the components in - you don't want too much direct heat. If no gas stove, a hairdryer or such will work also. Once again just be careful with direct heat - keep the hairdryer about four inches away and keep the dryer (air) moving. Be prepared to wait for at least of couple of days to make sure it is completely dry before reattaching it.
Good luck. Does it power up, etc okay, after the spill?
Check also that the RAM has been reseated properly and that no dust or fine hairs, or even fingerprints on the gold pins of the pieces, between the pieces and where they make contact with the ram holder contacts.
Did you recheck all of the cables? If those things were working properly before, then replacement of just the hard drive and/or dvd player, would not cause it to start happening. Make sure you didn't disturb any of the other cables while you were in there. Sometimes it just takes a nudge. I've been inside laptops that had never been opened before, and found cables that had loosened just over time and the movement of the laptop.
Also, did you "zap" the PRAM when you first started the MacBook up? The laptop might not be recognizing the new drive and software on it. Hold down this key combination (in the order presented) after pressing the power button, "apple control" + "option" + "p" + "r". It is usually recommended to hold them all down until the computer restarts itself two or three times - then release the keys and let the computer start again on it's own. I often hold them down for five or six restarts though, especially if the computer has already exhibited errors. See if that helps.