How do I change screen settings on my Technosonic lcd 3201?

I recently purchased a high integrity SVGA monitor replacement cable, now connected between my Compaq and Technosonic LCD 3201. When I use the AV to select VGA I get a message Out of Range appear. The tech guys where I bought the cable say I need to change the screen settings on the tv but I am unable to find any settings to do this.
Can somebody help?, I would be most gratful.