Why won't it start properly?

So my Macbook uni. is in a bit of a pickle. It won't startup past the grey loading screen. The loading dial appears and everything but it can't muster to get to the login screen. I've brought it in to the genius' (...) and they told me what I had feared most:

Along with the in-need-of-service battery I was already aware of, it could be either a logic board malfunction or a HD complication. I fear it is in fact the LB, however, since it won't even start up with the original system install CD.

Has anyone else encountered this problem? I'm looking to sell the macbook for parts so I would like to know exactly what I can and can't sell for a penny or two.

Thanks!