My Sony vaio laptop turns on but with a plain black screen but I can hear the fan running and power button is on. I took out the RAM and battery pack out yesterday but sinse I put them back on the problem has occurred. What do I do?
Reseat your RAM ("reseat" as in take it out and put it back in, and make certain it's inserted fully and properly). You may also want to try an EC reset/power cycle: With the computer shut down, remove the battery and charger, press and hold the power button down for 5 seconds, and then put your charger and/or battery back in and test.
If you continue getting the black screen, see whether you can get a picture on an external screen, if you have access to one.