Notebook won't power on at times

hi all,

I’ve been experiencing a problem with my Acer 6930G notebook which seems fairly common…lately, when I try to turn it on, it fails in doing so… this http://www.youtube.com/watch?v=_Q5xEZnJBZA&feature=yout... is what happens when it turns on normally…when it doesn’t, the NumLock and CapsLock led won’t blink, and it dies like that (the monitor remains blank, though the power button stays lighted and the HDD led blinks faintly every so often…other than that, no sign of activity…the cpu fan dies as well, but that should be perfectly normal because it does that also when the notebook turns on, and it works properly for hours during sessions (I’ve checked it and it’s clean, little dust, and temperatures seem fairly normal (60 °C/ 140 °F average or little less for cpu, gpu, mobo and hdd)…so I guess it’s a power issue…it’s been happening only sometimes (like 3 times this week), and once it powers on properly, I can manage to turn it off and on continuously with no problem …I never use the battery…when the problem occurred, the notebook powered up after 4 or 5 tries…strangely enough, a couple of times it did when I turned it upside down (I was checking the fan after having disassembled the case), I’ve read something like that but it seems pretty crazy to me and I don’t know if it’s just a coincidence… any clues?   thanks