Diagonal squares and grey screen freeze on startup

It all started while I had an HD monitor connected to my MacBook Pro 17" Inter Core duo 2.16Hz teh other day...

All of a sudden I got a series of multi-colored squares or rectangles all over the screen... Then the computer froze altogether. Upon restart, the rectangles are there again.

Now the startup sequence sometimes gets past the rectangles and onto the grey screen but then it just freezes there.

Ocassionaly it will make it all the way to the login screen and very rarely even let me log in momentarily, but soon after the artifacts start appearing and the computer becomes unresponsive.

This is the same if I try to boot from the OS install disk or from a external drive.

Any help much appreciated. I know this is not a new machine but it is my work computer and I cannot afford to replace it at this time. :-/

Thanks

- Carlos (MrP0nch02)

Here are 2 pictures of what the squares look like on startup.

<a href="http://www.flickr.com/photos/carlosag/5908369744/" title=" by Carlos Alfonso Gonzalez, on Flickr"><img src="http://farm6.static.flickr.com/5273/5908369744_936c53b37c.jpg" width="500" height="374" alt=" "></a>

<a href="http://www.flickr.com/photos/carlosag/5908369116/" title="Untitled by Carlos Alfonso Gonzalez, on Flickr"><img src="http://farm7.static.flickr.com/6008/5908369116_eebe2384d2.jpg" width="500" height="374" alt=""></a>