This type of behavior is normally caused by the onboard bios battery
failing. Pressing the del key either takes you to the bios setup or accepts
the current setup of the bios (not knowing your machine type....) If you
have to hit the delete key on a soft boot (power on reboot), there probably
is something else wrong.
If this is a desktop, turn off computer, unplug all cables, open case,
ground yourself to the metal inside the case and find the button battery
mounted on the motherboard. It may be held in place with a clip or a small
screw. Remove the battery carefully, note the number on the battery and
reinstall it (sometimes just changing its alignment slightly will cause it
to make better contact and allow you to use it for a few days longer.) Go
to your local computer store, Radio Shack, Best Buy or the like and purchase
another battery and install it the first opportunity. Simply leaving on the
computer will prevent need to hit the delete key each time you boot the
system.
If this is a laptop computer, you may find that it would be better to
deliver the laptop to a computer repair professional since a lot of these
batteries are soldered in place and simply opening the case can be extremely
difficult for the average person.