Laptops shut down sudden


Sep 2, 2013
hi, my old laptop (5 years) in some weeks ago started shutting down with no reason, the power just shuts off, idk if is overheat or PSU problem.
But now more, my new laptop, 1 year old, started crashing and shut down without any reason too, and it doesnt overheat, so why? plz help me. i have no dust, i bought a cooler for laptops double fan, and still crash and the only way to stop that freeze is just hold power off button, =(
PLz help.
old pc specs: amd athlon 64 dual core @ 2.2 Ghz, radeon hd 2400 xt, 4 gb ram, win vista premium x86, when i try get in the BIOS it power off itself!
new pc specs: i7 2670qm 4xcore @2.2 Ghz, 8 gb ram, gt 555m, win 7 premium x64.