Most likely, the shop was right and the whole motherboard needs to be replaced. However, if you can provide the processor model number, then it can be accurately determined.
If you're Running Windows 10, right-click on the start menu icon in the bottom left and then click on "system". A window will pop up and you will see the relevant information.
If it's Windows 7, in the start menu, I think you right-click on "my computer" and then click on "properties" to get to that page.