Hi theted
Before you go ahead, get the laptop back and try it with one RAM stick in turn. Also try Abarbarian's idea of installing a Linux installation CD (costs only a few pounds).
If none of this works get two more quotes for the repair. But it is essential to get in writing what you are paying for. Your current copy of Vista on the hard disk will not boot onto a new motherboard so a new legal copy of Vista would be needed - rescue disks, as provided with most laptops, will not work. You will lose all your files after a clean install but there is software available to get over this, but it all costs.
See my previous post regarding local shops wanting to replace motherboards when the fault was a loose stick of RAM and one really large company - I can sing the jingle but cannot remember the name!
If you decide to go ahead with a motherboard replacement remove as many coverplates as you can from the bottom of the laptop and mark the motherboard - just a couple of scratches will do.
If you think this is extreme, read the Daily Mail article where repairers were copying holiday snaps from customer's hard drives onto data sticks for fun and replacing perfectly good motherboards for £235.
Cheers
peahouse 05