Graphic Card causing computer to shutdown randomly.

It was the first thing that came to my mind but it wasn't issue. My PsU is 450w. All details on my profile.

This has been a issue in the past with these older Nvidia GPUs. It could be that the card overheated. I would first recomend reapply thermal paste to the GPU processor. This means removing the heatsink from the GPU. Then reattach the heatsink and try it. If it works then great and if it does not your not out of luck yet.

Also could be a bad PciE slot on the motherboard.

The other solution is lets say diffrent You take the heat sink off and place it in the oven. Yes I did say oven. You can find a guide and feedback from other people who have done this on this fourm. It does work in most cases. I would try this AFTER YOU HAVE TRIED EVERTHING ELSE. This is only if you are sure that your card had overheated.

As for your computer tech. It sounds to me like BS what he is telling you. A real teck can find the issue with 2 hours at most if he is at home and has a testing rig as all good tecks have. If it was you GPU that was bad he sould have tested the card in a testing rig with a diffrent PSU that he knows is good. Thats what I think.

Here to inform you all that my PC is working properly as it should with graphic card inserted. Freezes was due to faulty hard disk connecting wire which then I replaced and ran chkdsk. I reatttached the heatsink as described and inserted graphic card. Now my PC is working fine for one and half day which otherwise would shut down after 10 minutes. Thanks for all your help. Cheers!