I mean, a GPU cannot make the pc lock up.
Dyeing GPU 100%
This is either your CPU (idk how, could be the cause though?) or the HDD (stopping for some odd reason? head stuck?), although I wouldn't say that these are the cause until we sort out the GPU.
Check for physical damage in the gpu slot, any scratches or anything looking out of order.
Try the gpu in another slot if possible
Test the gpu in another computer (yours or a friends)
RMA the GPU then when they send you a fresh one install it, then update us, if it still has those problems reply back.