PC sometimes start, othertimes dont, mobo light flickering when not.

Hi there everybody. I have a question, quite similar to alot of other threads in here, but i haven't been able to a solution for my problem.
My pc have always worked flawlessly, until 3 months ago. It often get's moved around (From upstairs to downstairs), i always shut it down in the start menu. When i move it i turn off the psu (on the backside of the case) and wait till the Mobo light is out. Then i unplug the powercable followed by everything else and then i move it. Then about 3 months ago, i moved it downstairs and it could not start. There were no fans spinning, no reaction at all. I switched off the psu, unplugged, waited for 10 sec, plugged, switched on the psu and it suddenly started. After that i could move it as normal without any problems. Then suddenly one day the same thing happened, i got it working after about 1 minute and don't remember exactly what i did, (Nothing inside though) Then about a week ago it would not start, no matter what i did. I opened the case and checked everything inside, nothing. I then noticed that the mobo light was "flickering" and did not glow as much as normally. I tried everything nothing changed, i got frustrated and waited for an hour and PC just turned on.
3 days ago it happened again, but this time it wouldnt start, not after an hour, but after only after 9. I changed some bios settings, made sure the wiring was ok and when i took it upstairs one day later it could start with no problem. Now i just took it down again and guess what, not starting. This is frustrating me and i have checked wiring, pins, psu (paperclip) and i can't seem to find the problem.

I don't know the exact internals but it is an asus p6t-se motherboard and a thermaltake 750watts psu. 8 gigs corsair ram and a HIS 5870 graphics card.

I would really like some help or ideas on what the problem is, how to fix it, or how to just turn on this frustrating pc. Why does the light glow correctly some times and not other times even though i do everything the same? I really don't understand what is happening as everything seems fine, and when it starts, well, it runs like it always have.

Any help appreciated!
Alex.

But why is it that this only happens when it disconnected totally? When it finally get's running i can have it on for 3 days straight, then shut it down, and turn it on the next day and run it for 3 more days, shut it down, turn it on next day and again it keeps running? If the psu is not delivering a "steady" power would it not shut down at some point, atleast have notable descrease in power when playing or any other signs?