Inspiron 1521 won't boot up. fan kicks in then shuts down nothing comes on screen

I'd replace the fan motor.

check if cpu fan is working , remove if any dust is stuck in it , if the fan is having a problem try replacing the fan , add heat sink paste if required

there are two settings in the bios that need to be changed....one is the automatic sleep/shutdown and the other is the remote wake-up

OverheatingWhen the CPU overheats then it will shut down (i.e. thermaloverload) and won't boot up again until it has cooled down. If this is theproblem is not fixed then the CPU will eventually fail.
A faulty fan causes the problem or the fan and heat sink assembly are cloggedwith dust.
Check the CPU fan to see if it spins freely, if not replace the fan.
If the fan and heat sink is clogged with dust the remove the dust and make surethe vents are clear and dust free. Use a small brush and can of compressed airto do this.

try to change your ram maybe it will work

Check the power source and make sure the cooling fans are not clogged with dust and lint. Laptops will just shut down if they are over heating or not getting enough power.

When the charger is plugged in, is the charge light lit up?

If you laptop appears to boot up and the hard disk LED flashes then the problem could be a back light problem. This could be a faulty inverter or a faulty CCFL lamp. Please click on this link to determine the fault and possible fix :-
http://www.fixya.com/support/r3598095-faulty_laptop_lcd_screen

do some google searching. Most laptops have a jumper that can be shorted on the mainboard to reset the bios password. also, some programs have been written to do it as well. Google is your friend here

THis sounds like a power supply issue.. I had a similar issue with mine. my fan would kick on for about 2 seconds then shut off.
Hope that helps 
Ciza