My dell optiplex 330 starts for one second then shuts down and reboots vicious cycle

There are many issues that could cause this: corrupted login profile, errant command in the startup routine, virus, stuck key on the keyboard, stuck power button, and more. Without more details, it is difficult to diagnose this. Even with more details, it is not terribly easy to diagnose this from afar. I would suggest getting in touch with a local computer repair shop and see what they can do for you. If you happen to be in the northeast Kansas area, let me know and I will be glad to offer my professional services to assist you.

Installing a fresh operating system is a good option, and there might be a feature in the BIOS to restore the system to factory defaults. Information on how to do this:

Windows XP: Dell PC Restore

Using PC Restore:

1. Turn on the computer.

During the boot process, a blue bar with www.dell.com appears at the top
of the screen.

2. Immediately upon seeing the blue bar, press <Ctrl><F11>.
If you do not press <Ctrl><F11> in time, let the computer finish
starting, and then restart the computer again.

NOTICE: If you do not want to proceed with PC Restore, click Reboot.

3. Click Restore and click Confirm.
The restore process takes approximately 6 to 10 minutes to complete.

4. When prompted, click Finish to reboot the computer.

NOTE: Do not manually shut down the computer. Click Finish and let the computer
completely reboot.

5. When prompted, click Yes.

The computer restarts.
Because the computer is restored to its original
operating state, the screens that appear, such as the End User License
Agreement, are the same ones that appeared the first time the computer
was turned on.

6. Click Next.
The System Restore screen appears and the computer restarts.

7. After the computer restarts, click OK.
or

http://www.user-guides.co.uk/download/dell/delloptiplex/dell-optiplex-330-reset-bios-password.html

Dell Optiplex 330 Desktop Product Video http://www.youtube.com/watch?v=K3CDVOZMVpo DELL (OPTIPLEX GX520/320/330) http://www.youtube.com/watch?v=xbaDqnoDNP4 Unboxing & Setting up My Dell OptiPlex 330 http://www.youtube.com/watch?v=LX_-y8Y9WcY Dell Optiplex Computer Powersupply issues.MTS http://www.youtube.com/watch?v=dzSCXgvAFGg

Sounds like hardware failure. Could be the anyone of the many components inside of the computer. It's definitely not a software issue.

My suggestion would be to take it to a tech or buy a new computer.

Try shutting down the computer, unplug for 30 seconds or so. plug in reboot. If that fails, reboot and start the restore/recovery software using the F key. this may help: http://support.dell.com/support/edocs/systems/op760/en/sm/systemse.htm#wp1157779

Dell Support > Optiplex 330 desktop computer > Drivers and Downloads,

http://support.dell.com/support/downloads/driverslist.aspx?c=us&cs=19&l=en&s=dhs&ServiceTag=&SystemID=PLX_PNT_330&os=WLH&osl=en&catid=&impid=

(All versions of the Optiplex 330 are covered)

Click on the blue down arrow to the left of - Networking

Regards,
joecoolvette

See whether the cd is damaged.

your powersupply could of gone bad try to unplug the powersupply and plug it back into the motherboard if this doesnt stop it the part of the powersupplly that tells it to kick on is bad

Try to clean the RAM and place it again in the motherboard.

The processor speed may be too high or too low for the computer to handle. It can become reset to a default choice when you reset the BIOS. Just keep changing it until something works. (There should be around 3 choices)