My computer has worked fine for 2 years now, but when I should start it up one day a week ago the pc-speaker beeped like a siren and the screen said "BIOS checksum error". When I reset the same text appeares but with an extra "INSERT SYSTEM DISC IN DRIVE A:" or something similar. I reset again and the usual BIOS screen comes up and the memory counts up, but then everything locks up. I reset again and the memory counts up and the IDE-units are identified but then everything locks up again. I reset again and this time I come a bit further in the boot sequence but it locks somewhere while booting windows. After numerous resets the computer works like a charm though, but I have to go through this process every time I start it up.
I have cleaned all fans, thinking it could be an overheat problem, it didn't help and the temperature is the same as it has always been. I have upgraded the BIOS to the latest version but it didn't help. I have also bought a new CMOS battery which didn't change anything.
I did no hardware nor software change prior to the faults appearance.
Could it be the power supply? Or possibly the processor fan needing a start-up time?
I'm grateful for any suggestions because I am rather clueless. Thanks in advance.