What do I do with 3-1-2 Master DMA register failure?

[Huios]

I took my tower in to get fixed only to get it back more broken than before. It has
" video input no signal" on monitor when I turn the computer (dell optiplex 745 tower) but it has a series of 6 beeps also when I turn it on, which weren't there before I took it in to get fixed :/ help me.... And can I fix this problem myself?

 

[Phillip Corcoran]

6 beeps on a Dell = Video BIOS Test Failure

In other words, the graphics card has died, which in turn causes the "No Signal" error message.
So you'll need to install a new graphics card.
DIY? Certainly.