As I have just purchased a new laptop and as my nephew needed a PC for his school work I decided to sell him mine and donate the money to a local charity.But they ave now returned the PC saying it is full of viruses and does not have office.That is strange as I had the PC checked three weeks before I gave it to him.Anyway I put it all together to see what the problem was but when I pressed the power button on the case it was loose and on looking inside saw it was dissconnected (Broken )but was still able to start PC by pressing the actual switch stem inside but although the PC starts up the monitor says no input signal.I have connected the ethernet cable from the router to the PC.The router is a N ADSL2 + the ethernet cable is plugged into socket Lan 3 but the LAN 3 Led is not lit.Sorry so long anyone any ideas as to why there is no input signal
Also check if it is using the onboard graphics or a separaet graphics card. The number of times I've connected the VGA cable, seen the same message and then realised there was a graphics card installed ....
I have just taken it back to the PC shop I use and they checked it and said the hard drive has packed up.Not sure what to do is it possible to just replace the hard drive or as they say not worth the expense.Seems a shame too just get rid of it for the sake of the hard drive.
Perhaps a re-statment from someone closer to your know-how than the expert advice others have offered.
Power switch has been mauled but you have found a workaround for that.
The VGA cable might be faulty, they do go open circuit after long use with meddling.
The VGA cable may have been plugged into the wrong socket on the PC. If there are two sockets with identical plugs try the socket away from the others, coming from it own "slice" on the back of the PC.
The HDisk would not normally affect the monitor until Windows starts to load. Even if the HD has failed the display would usually work through the BIOS section and hang at the point where Windows should start. At that point it would say something like No bootable disk.
So I think like the others it is a VGA -Monitor problem Blank screen after switch on needs curing first.