How do I get rid of the checkerboard grid on my files?

Question

I have just bought an iMAC 21.5"  and installed my CS3 photoshop program.
When I used it on my old iMAC 20" every file had a white background.
Now every file has a checkerboard pattern or grid -- very small. Drives me crazy.
They are also on the little thumbnails on the Layer list.
There must be a way to delete this "screen" "grid" but I cannot find it on VIEW or anywhere else.

Answer 1

Thanks for getting back to me!
My 7-year-old iMAC 20” blew up on Friday AM — CRACK!!! and smoke issued forth.
A techie friend suspected it was a power supply component
and hoped my HD & two External HDs survived the explosion. (They did.)
So I bought a new iMAC 21.5 and re-installed CS3 from disc.
Any new files I created since the CS3 re-install were fine (WHITE already clicked on.)
It was all my old PS files (hundreds of them) that Opened with the grid present
after the reinstall of CS3 in my new computer. They had not been created with a grid.
As an artist I was frantic as the checkerboard effect was impossible for me to work on
and simply adding a layer of white underneath did not resolve the layer thumbnail images
which were a strip (my files can be 600 layers) of tiny checkerboards.
          I have resolved the issue using this advice from an artist PS user friend:
          Go to Pref. in Photoshop — then Transparency & Gamut — 
          I made the grey checks into white using Custom.
What I am now troubled with are the FONTs this CS3 re-install on my iMAC 21.5 has eliminated
causing me no end of work to fix. Six of my favourite fonts. Gone.
O well. Perhaps I will find I have been given beautiful new ones to play with.
Thanks again, Brett.
Barbara Carlson
Ottawa, Ontario
http://www.barbaracarlson.ca