Odd display issue

I've got this really odd issue in my display all of a sudden.
I've got Windows XP on a PC.
The lower left-hand corner of the desktop screen (looking at it - where the start button is located) has turned purple.
The colors of the start button are now purple and any window icons that that are opened in the taskbar in that area are also purple. The little arrows at the bottom of pages are now green where they used to be gray.
Nothing else is affected - the pages in my documents are all white and normal as are any sites that I look at.
I did nothing - I changed nothing - I've got no idea how or why this happened.
Any ideas why it happened and how to fix it?
Thank you.

 

Sounds like a dying video card. Will shut down waiting some time and cold boot t emporarily resolve the issue?

 

Will shut down waiting some time and cold boot t emporarily resolve the issue?
Nope - this happened on Friday and the computer was off until today and when I put it back on it was the same.

 

It has to be either the video card or the monitor. What is your video card?

 

Try a different monitor.

 

I've got no idea what video card is installed - where will it show that?
I've only got the one monitor.
If I need to change the card which (what specifications) do I need to buy and is it easy for soemone who has no knowledge to install?
I've got a Dell Dimension 4550.

 

Sounds like an Agp 8X card. It's one screw and slide out slide in.

 

Sorry for the delay in getting back but is there any way of knowing that that is definitely what needs to be replaced before buying the new card?

 

Run this:
http://www.gtopala.com/siw-download.html

 

Well - my computer has been off since Friday (I'm observant and don't use electronics during Passover) and today when I turned it on - the purple was gone! Everything is back to the way it was before.
So weird!