I recently had a dc input repair in my laptop. While it was in the repairers the Radeon HD7970M card stopped working. I cannot prove that it wasn't working before I took the laptop to the repairers, however, I know it was otherwise I wouldn't have been able to games correctly.
If I can offer proof then they will be liable to replace the card if they cannot get it working again.
Is there a place in the laptop memory where there will be a record of the operation of the gpu card, i.e, a date & time recorded when it failed, like an error log? This way, if it was in their possession when it stopped working we have definitive proof it was there doing.