Hi mate
if it turns out to be the motherboard, dont scrap it...
i had my motherboard killed during a software update and i had everything inside it changed to Version H internals for the grand sum of £230, this was on top of what it cost to ship it to him in the czech republic, PM me and i'll send you his email address, guy really is absolutely amazing and comes with fantastic credentials - 'josi', 'peter_chicago' on the vwnavi forums all know him, i think the chap works for continental (the company that makes the units) he'll be able to fix your unit without any problems
but by the sounds of it yours may just be a loose cable!
good luck with the repair, feel free to PM me if you need any help!