What exactly does it say when it starts up? F1 can be the BIOS utility, or it may say "blah blah happened, hit F1 to continue", or a few other things depending on the BIOS brand and PC brand. We need to know the blah blah part.
Considering the age of your computer, you may want to replace the CMOS battery, they are very cheap. Could be your BIOS is not able to save settings properly. Also do yourself a favor and upgrade to at least 1 gig of RAM, running anything on 256mb of ram now is like using a horse and buggy to do farm work these days.