Feel really supid here.  I changed the powersetting on my display.  this is what i did:

opened display, clicked on screen saver then power
Clicked on UPS
chose APC then back-ups
then hit configure
and then when i saved it the computer started shuttiing down and I couldn't get it to stop.  Now the coputer will start then start shutting down.  I don't know what to do.  My start up disk doesn't work.  I get an error message when I try and use it. 

My computer is a Compaq presario with 60GB hardrive, CD-RW/DVD-ROM combo drive.  The system is XP home.

Thanks for any help you can GIVE me.  You know the old story, money is tight and I don't want to have to spend it in a shop if I don't have to.  Thanks again for reading this.
Do you actually have an APC UPS?What settings did you put in the Configuration screen?  Can you start in Safe mode?  To do that, As your computer restarts but before Windows launches, press F8.  2K_dummy:  Yes I have the battery backup device. 

Soybean,

I'm not sure of all the settings. I think that they were:

enable all notifications

CRITICAL alarm
minutes on the battery before critical alarm 2  (this was already set)

NEXT instuct the computer to: shut down

 

 I'll try your suggestion and will report back once I've tried it.  thanks for your help.

CharliI tried the F8 and f10, neither work.  F1 does but it doesn't help me at all with this problem.  Thanks,  any other suggestions?DISABLE the screen saver...Can't get in to do so.  If I could get in I could change the display settings. 
as soon as the windows start up and I try and click on display it gives me an error message saying the system is shutting down.

Thanks anyway.  Any other ideas???
When you pressed F8 during startup, did you get an option to start in Safe Mode?  If not, try that again.I can't get into safe mode when I press F10 or F8.  Only F1 works.  I've tried several times several different ways (ie pressing when I turn it on, pressing and holding, etc).  Sorry but that just didn't work.  It's very strange.  Thanks again.Someone on another site suggested I UNPLUG the UPS unit.  I disconnected the UPS and for some reason that allowed me to go into safe mode where I was able to change the display back to it's original settings. Thank you so much for all your help. Thanks everyone for all your help and suggestions.