Mac Pro strange boot error

I was using my mac pro 3.2 octo from 2009 without any troubles.Recently it started giving non stop trouble.I have 2 gb ram from the factory and another 2 from 3rd party.My problem is when I boot my mac I am getting some strange vague designs and it freezez.I tried shifting the boot hard disk from slot 1 to slot 2, booting with either set of ram,changing the graphic card slot etc.Please help.

Thanks in advance,
Thomas.

That's the sign of a possible defective graphics card. Do you have another you can substitute in its place to test whether or not it may be the problem?

Don't think it will help much but you might try the second monitor connection if your card supports dual monitors.