Might be a problem with the AC adapter? Or quite possibly the motherboard.
If your laptop boots up using the AC adapter without the battery, try removing the battery and placing it back in while the laptop is on.
PC2-4200 is the rated speed of the RAM. It is how someone can determine how fast the RAM is. For more information on RAM http://en.wikipedia.org/wiki/DDR2_SD...tion_standards
Check eBay, it seems to have good priced Hynix RAM
Google search comes up with the RAM as a Hynix brand. Any SODIMM PC2-4200 RAM will be compatible with your current stick. Search around eBay or craigslist for the RAM. I found one for a good price but it is in Canada....
Were you sure that everything was dry before power on? Sometimes components will work for a bit and give out without notice.
It may be a loose connection if you opened up the laptop to clean it. Make sure everything is connected correctly.
Usually you are able to hear the hard drive spin up on boot-up. But that still does not solve your problem, even with a bad hard drive the computer should still POST (white text on black background).
Loose connection between the LCD and...