Date & time Settings

sounds like the coin cell battery on your motherboard needs replacing. watch the black screen carefully at boot, see if you aren't seeing an indication it needs to load defaults or something.
then if you post your bios these rabid hardware folks will tell you how to replace the coin cell. all i can tell you is, if it doen't come out easily, don't force it. sigh. or you will have to learn to solder

Sounds very much like the beginnings of a flat battery so you should change it now before you start getting some real problems.

Just remember to power down and remove the mains lead and then leave the unit stand for about 10 minutes to make sure that you have discharges all the capacitors and it should be an easy job to change the battery, just take careful note of the way it came out and put the new one in the same way.

If you leave the mains lead in and drop the battery it can short out and destroy the M'Board.

Col

Give answer # 1 the points, your battery is dying ! But if it is from the Win 98 era you may have problems finding the velcrowed battery you will find plugged into the motheboard ! (Usually on the side of the power supply !)