What it's almost certainly telling you is that the CMOS battery on your motherboard is dead. That means that e.g. the date and time have been set to whenever the mobo was built, and asking you to press F2 to set up is asking you to go into the BIOS to set the right date and time. You can ignore it and press F1, but that may give you problems down the line with a mismatch between what date/time your PC thinks it is (from the BIOS setting) and what date/time it really is. Replacing the CMOS battery is pretty straightforward - but if you don't fancy it, you'll just have to accept resetting the date/time in the BIOS each time you power the PC on.
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