Hello my pc has a big problem i switch it on and it switches back off within couple mins and its always black screen nothing d

There could be several causes to your display issue. Here are the most common:

1. Bad or misconfigured RAM
2. Bad or misconfigured GPU
3. Electrical short
4. Bad PSU
5. Bad CPU
6. Bad mobo

Start eliminating possibilities by using the no boot/no display troubleshooting guide (link in my signature).

If the problem persists, post back with the troubleshooting guide as a template.