A emachines c2825 pc with windows XP (and a MSI KM4M / MS-6734 motherboard) runs xp for about 4 mins, then suddenly loses power. Then you can hear a strange noise coming from the motherboard -- a faint hum or whine, which alternates between two frequencies kind of like a french police car siren. When I unplug the power cord or the p1 connector, the sound continues for a few seconds and then stops.
It takes an bestec ATX P4 250w psu. I replaced this with a dell ATX P4 250w psu. Then when I power it up, the boot process doesn't go beyond the first screen (the "e" for emachines -- before POST). And if I leave it like that for a few mins, the same thing happens anyway -- I lose power, and get the sound.
I tried another replacement psu (a third psu) and the same thing happened (emachines "e" logo til it turned off and I got the whine).
It seems like the longer the PC is on (the more often I try to make it run), the more frequently / quicklly it crashes and makes the noise.
(1) Has anyone heard of this noise before and knows waht it is?
(2) Why would one PSU boot it to windows (until it crashes) and two others make it hang on the blue e (until it crashes)? Why the difference?