You have to be patient and troubleshoot in a logical manner.
First..... List all your sys. components in your profile( so they show at the bottom of your post)..... like the other posters in this thread.
Your system was up & running, then something happened; could be almost anything. So you have to try to isolate the problem.
2nd......... I would try to just POST with 'barebones' components...... mobo, video card, only 1 stick of Ram, no drives.
If you have a 'D-bracket' connector for diagnostics, plug it in......... @ led failure test.
Listen for the # audio beeps, check what the screen says, and check leds, if you have the bracket.
* take your time.