What do I do if my computer's motherboard is dead?

I was having many problems with it for the past year. It’s been in and out of the shop and the guy said he replaced my hard drive. It worked for a couple hours, then blah… I took it back to the shop and the guy took it for awhile and told me it was my fried motherboard. Is it worth replacing it? Also, my brother told me that if the guy took my hard drive that he had all my data. Is that true? It seems shady. I wish I wasn’t so dumb with computers!