Hello Selsong, welcome to SF!
A couple of questions.... I guess the store checked your pc before and after replacing mobo right?
You have limited your info a bit in your post so I'll go with the two most logical scenarios:
1. shop just believed you and could not, or did not even try to replicate the problem before mobo replacement. But DID show you it worked fine with the new mobo. Once home, the problem returned.
2. Same but old mobo proved to be faulty in the shop.
In both scenarios there is a chance that you have a power and/or external connection problem. The latter means stuff you add to the system that you did not take along to the shop to test as a whole. If you think this is possible, check your house power connection, if needed be sure to have a surge protector, take out any external extra stuff and test just like in the shop....
In the second scenario there is also the possibility, in case of infrequent bsods tht you just happened to not get in rhe shop, that you have conflicting powerplan / BIOS energy saving settings.
But... The reason for this story is... In my humble opinion, as it is a new system that came with Windows 7 out of that shop....ONLY the home powerreason would stop me from returning it under warranty asap.