It is a Compaq Presario V6000 model.
When the A/C adapter is plugged in, the ring around the plug jack is lit and the icon for charging the battery is lit also. When I press the power button to start up the laptop, the rest of the icons light up in blue and the fan comes on. After about 20 seconds, the laptop reboots itself automatically and continuously. This reboot sequence happens every 20 seconds until I hold down the start button to force a shutdown.
During the 20 seconds of this start up, and only Compaq logo come up. I only hear the fan, no other sounds.

Any ideas before I start taking it apart to check for loose connections?Try it with the battery removed....wait 5 minutes and hook up only mains.
See if it's still doing the restart.Yes still its restart
What changes or issues prior to the problem at hand? Have you tried going to safemode to skip the restarting problem?only Compaq logo come up and when i press F10 for BIOS Setup it gets hanged OK providing you have tried the obvious hitting f8 (safe mode)
It sounds LIKE it might be a hardware issue such as ram cards failing and could cause it to restart; Add to this the fact that whatever is wrong could be an expensive part of your PC to replace - like the motherboard or CPU. You may be facing anything from an electrical short to a serious hardware issue.

Do you get a beep CODE when the COMPUTER turns off; if so how many beeps?
Just in case make sure you have the correct power cable.


Check for electrical shorts inside your computer. This is very often the cause of the problem when the computer powers on for a second or two but then powers off completely. Take you time!

Reseat everything inside of your computer. Reseating will reestablish all of the connections inside your computer which may have wiggled loose over time. Harder with laptops but should be able  to get at the ram and harddrive. Reinstall each piece of nonessential hardware, one component at a time, testing your computer after each installation.

Hope this helps but you may have to send it away  It's a laptop...
Other than the RAM and HDD there's not much more to remove and re-seat.