My computer desktop will not display.

when I power up my computer the display turns white and nothing displays. I"m told at the genius bar that I need to replace my logic board because of enlarged or blown capacitors. If so they want a large amt of money for the part and labor. I have grown very attached to this computer and would like to save it but the cost is a little over the top any suggestions how I can get this repair made at a reasonable price? I looked at a step by step guide on this site and while I'm not the most computer literate person I think I might be able to do this myself with a little help which in the grand scheme of things saves me about 150.00 and makes it more reasonable. How do I know that this is the only thing wrong with the computer?