monitor switching off on its own

Archived from groups: comp.sys.ibm.pc.hardware.video (More info?)

monitor = Nokia 447ZAPlus
g-card = geforce4 MX 440

what happens is that ard 15-20 minutes after switching the pc on, the
monitor goes off.
Its like its hitting an auto-fuse or something. The on indicator is on, as
if the monitor is operating as usual, cant get the monitor menu, so i goes
its not transmiting from the crt tube.

If i switch it of and wait for a while, it comes back on but it doesnt last
more than 15 minutes at a time.

It is an old monitor (4 years ) and unfortunately its not supported anymore
as Nokia are not making computer monitors anymore.

Does anyone have an idea what might be wrong?