macbook pro startup issues

this is my first time posting anything on here, altho i have read a lot of the threads on this site,
awesome site guys. i am averagely knowledgeable about macs so i will try help out where i can.

ANYWAYS

i have a macbook pro 15" intel core 2 duo 2.33ghz 2gb ram(stock) and im running OS X10.5.2.
yesterday i go to turn it on and i hear the fan come on and the beginning of the startup (2/3 seconds) then a power down sounds like a faint beep dead nothing nothing on the screen blackness.

it does this with the power cable unplugged, if i turn it on with it plugged in, it starts and seems to sit and do nothing, black screen, no sounds, just a very faint hum of the hdd or fan. i have left it like this for an hour and nothing happened.(i know its not booted as i cant access the hdd over my network with my other mac.) then i hold down the power button for 3 seconds to turn off, power down sounds like a faint beep. off.

i have got it randomly to boot a few times, the last time i was pressing the power button while turning the macbook on its side ( i read that it might have something to do with the motion sensor in the hdd, not sure about this thou)

so now im using it and it works fine, so long as i dont turn it off.

i have tried:
reset the pram
swapping ram,
other ram,
power up with ac power
power without ac power
power up with ac power and no battery
startup with every key combo, s,c,v,t,option,command,shift.


any help would be awesome, im really stuck with this

thanks

Try updating OS X to 10.5.3 (now available on software update).

update installed and still having the same issue,
is this job for apple or can i fix this?

Have you tried resetting the SMC or the Apple Hardware test?

ive tried resetting the SMC, didn't make a difference,.
trying to figure out now, how to run a hardware test with out the original disc, as i have left them in england,(i currently live in the US.)
BUT
i have figured out how to turn my macbook pro on, and seems to work nearly every time, by picking it up tilting it backwards and to the right, and then press power and it boots, and works with out a hitch, until i turn it off, or twice now it wont wake from sleep.

so if this and issue with the hdd? motion sensor's?
i noticed in system profiler, under motion sensor is say "enabled" is there a way of disabling this? and if i did, might this help, or is it better to leave it on as it does help power up my mac.
any help would be awesome,
thanks to all who have reply, thanks alot

http://docs.info.apple.com/article.html?artnum=300781

Give this a try. ?
http://docs.info.apple.com/article.html?artnum=300724