Check the diagnostic lights on the back of your system, what ever your system is ?, see if they are not all green.  Run a systems Hardware diagnostic test for your system to see if anything is broken.   Update your anti virus software, run it to see if you have a virus.  Download and install a good spyware program, run it as well.  Did you install anything in the last day of so that might be the problem.  Many things you can do to check, but we cannot assist you if you do not list your systems model number, operating system, memory and video spec's as I have done below.

Dim 4400 ( June 2002 )
2.6 ghz (upgrade from 1.7 ghz)
768 MB 2100 DDR Memory
Gainward Ti 4200 128 MB Nvidia
XP Home plus SP-2
17 inch Dell LCD monitor (1703 FP)
48 X CDRW
AVG 7.0 Anti Virus
Zone Alarm Free Edition

Boy you really have an older system.  Its a P-III, is it not, that came out around 1999 ?  ( I think  you  have 256 Mb of memory and not 256 K of memory) .   I have looked with a Google Search and came up empty, I went into the Dell data bank and could not find your system.  Unless someone on this forum has that computer or knows enough about it, I would suggest calling up Dell right away and see if they can assist you.  You may have to remove the memory, one stick at a time to see if it boots up. If it does boot up, than its a memory problem.  If not, than you will have to remove or disable the other hardware one at a time to see if the system boots up then, ie, the hard drive, cd player or other connected peripherals.  If this is not the problem, it could be the motherboard.  I am sorry, but I cannot think of anything else for you.  Hope someone maybe able to help later.

 http://support.dell.com/support/downloads/devices.aspx?c=us&cs=19&l=en&s=dhs&SystemID=DIM_PNT_P03_XPS_T___&category=0&os=W98&osl=EN  This I believe is the download site for your system, not possitive, for any diagnostic software and other stuff that you may need if you get it up and running again.

Dim 4400 ( June 2002 )
2.6 ghz (upgrade from 1.7 ghz)
768 MB 2100 DDR Memory
Gainward Ti 4200 128 MB Nvidia
XP Home plus SP-2
17 inch Dell LCD monitor (1703 FP)
48 X CDRW
AVG 7.0 Anti Virus
Zone Alarm Free Edition

Message Edited by SR45 on 01-12-2005 02:59 PM

I do think this link will take you to your system to the best of my knowledge.  Click on the link and then click on system codes.  You will now see the different code lights for that XPS T600 system.  It tells me very little except that there is a failure somewhere.  It keeps telling me look for " Getting Help " in chapter 7 of the reference guide for the code error that you see onback of the system.  Cannot find the darn guide.  Tell tech support the problem but when they find out the warranty is way past they may request that you call a pay phone support instead.    

Message Edited by SR45 on 01-12-2005 05:37 PM

I dunno wut dot means. Dot specific Led code is somethin' I haf not heard of. It could be anything...like loose cables on the Hard drive or the CD Rom. It can also be because of the Video drivers having gone corrupt. If you are good at dismantling and reassembling things, then open the computer, unplug all the cables and reseat all the expansion cards as well as memory cards.

Ah hope dot works.

Got it working

Had something to do with the USB port hookup.  Had to go in and delete  through Device Manager, then got it working again.  Thanks to everyone who responded.