When I start my computer, I get an error stating CMOS checksum error. Press F1 to contine. But this happens only some times. WHat is the problem?

replace your cmos batterie it sounds like its on the verge of dying.

It certainly sounds like the CMOS battery is dying!

Without a battery in good condition, your system configuration data is not being stored, and it is needing to run setup to detect the equipment installed in the PC. Running for a period of time will charge the battery somewhat, ensuring that configuration data is retained for a while. this explains why it starts up fine sometimes.

But left turned off for a period, the battery will be going flat again, and the dta will be lost. replacing the battery is a simple and inexpensive process on most systems.