I have a 300 watt PSU powering AMD Athlon 64 3000+, 512Mb PC3000,
GeForce 6600 GT AGP and a seagate 200 gb sata drive. Nothing else at the
moment. Sometimes the computer will just fail to start even though
nothing has changed since the last time. I have to clear the CMOS and
even then it will sometimes not work.

Could my PSU need an upgrade?

Regards

Dan B