Will not boot up - Asrock P4I45E-R3 P4 845E FSB800 DDR400 Motherboard (MOTASR15)

Computer does not boot up The problem maybe the RAM, it is faulty or just needs reseating to make proper electrical contact.
Reseat the RAM and then boot up your laptop. If it still does not boot up then remove the RAM module/s and take them to your friendly computer repair shop and get them to test the RAM for you. Just like you sometimes need a mechanic to repair your car, sometimes you do need a technician to diagnose and identify the fault or faults on your computer. Not only does a good service technican have the experience to deal with this type of problem, they also have the equipment that allows them to look at things the average computer user can't see, and he has a collection of replacement parts that can be used to quickly test individual components on your computer.

Also, in addition to advice on RAM, your hard-drive may be shot. This happened to me with an old hp computer. It only had 42 gigs of drive space and about 256 mgs RAM. Even though I upgraded the RAM to 512, eventually I could no longer boot. If you upgrade the RAM and still have problems you can add a good hard-drive compatible with your pc limitations, then make the old hard-drive a "slave" or secondary drive. This should solve the problem.