several reasons may be the cause
1. New hardware has been recently installed.
2. Error or confliction with settings in CMOS.
3. CMOS battery is bad or failing
If new hardware has been recently installed into the computer, it is likely that you are receiving the prompt "Press F1 or F2 to enter setup" because CMOS needs to verify that the new detected hardware is properly being setup in CMOS. Enter CMOS setup and save the settings and exit.
If no new hardware has been added or you continue to get this prompt verify no error or conflictions exist in CMOS. Press the key to enter setup and verify that all settings are correct.
If your time and date are not set correctly, your battery is more than likely bad. Try setting the correct time and date, save the settings and then reboot. If after turning off the computer the time and date get reset again replace the battery.
If the time and date are correct and everything else appears to be correct try
resetting the CMOS values to the defaults.
If you continue to receive the prompt to enter setup each time the computer boots up and you have attempted to follow the above suggestions, your CMOS battery is probably bad. Replace it.
HTH
ah, SATA drive ... turn off PC, open case, check cable hasn't fallen off or become loose ... several of us here have had that happen and now use a hot-glue-gun