MY chassis fan went out. I replaced it. Now , I get the "no signal, check connections".what did I do wrong?

That's an indication the display isn't getting a video signal from the computer.

Check the cable that connects the display to make sure it's still connected properly. Look at the display end of that cable to make sure it's connected there too, although some cables aren't designed to be disconnected from the display.

If you have a notebook/laptop check the owner's manual for key combinations that select between the built in display and external displays. If you are dependent on an electronic user guide you may have to go to a public computer like at a library or web café and look for a manual on the manufacturer's web site.

Note that some displays double as speakers and even microphones too. The "No Signal" message concerns the cable that typically has a rectangular or trapezoidal connector and over a dozen contact pins. The audio cables usually look like portable CD or MP3 player headphone plugs.

Either try the display on another computer OR try a different display on the computer.

Did the computer original produce a single beep before loading the operating system ?

Does it beep multiple times now? Multiple beeps usually indicate a problem, but the beep pattern varies depending on the motherboard manufacturer's choice of BIOS (Basic Input Output System)

My Speakers Stop Working In Sudden I Bought New Ones And No Sounds:(