Random Desktop freeze - Ubuntu 16.04 - GeForce GT 740

I have random desktop freeze with Ubuntu 16.04, GeForce GT 740 and driver version 415.18

here the result of nvidia-bug-report:

You’re getting

[  358.033778] NVRM: Xid (PCI:0000:01:00): 79, GPU has fallen off the bus.

That’s a hw failure, can be due to overheating, lack of power, …
Start by checking temperatures using

nvidia-smi -q -d TEMPERATURE -l 2 >nvtemp.log

If that doesn’t show any anomaly, check the pci slot, reseat the card, change slot, check psu.

Thanks for the answer.
I don’t think the problem is the temperature because I got desktop freeze even with GPU at 25C.
I swapped the PCI slot and I have the same problem.
It remain to check PSU. Is there a software tool to do this?

No, you can only swap the psu. Might of course also be a defective graphics card, so check it in another system.