This appears to be a defective infrared cutoff filter, and it is a defect seen on many D80, D40X and D60 Nikon image sensors . If you pull the filter and check the bottom under magnification, it almost looks like micro drops on the bottom side of the filter, like the coating didn't stick or is now coming off. It appears to be some sort of manufacturing defect - possibly contamination during the coating process on the bottom layer of the filter. Unfortunately there is nothing that can be done for this other than replacing the image sensor, unless you want to convert your body to infrared. Nikon never sold the cutoff filter separately, and now that Nikon has stopped selling parts you can't even get the complete image sensor. As usual, Nikon has never acknowledged the problem . . .
Most likely cause: Impact to the flash caused the release side flash pivot to fall into the camera body. A small plastic bit on that pivot closes the flash-up switch. This is a well know problem with almost all Nikon DSLRs. The pivot is hollow and the wires from the flash head go through it, so it is possible to carefully fit a very small hook in the hole and pop the pivot back into position. Make sure you don't break any of the small wires! There are two screws on the underside of the flash. Remove them and then you can pop off the cover with a fingernail
Check to make sure the 'bars' on the shutter are all the way to the left and invisible. If you can see them, try pushing gently with a fingernail until they slide all the way left. This may unlock the camera. Check the release capacitor on the bottom. If you see any green on the leads it is bad - heat one of the leads with a soldering iron - if you smell 'fish' then it is bad. If leads have leaked onto small circuit board, try cleaning with isopropoyl alcohol. If leakage is too bad, board will have to be replaced. Part is of course no longer available, as Minolta is out of business.
This is usually caused by a loose screw (one or more of the screws holding the DC to DC board on the bottom). They can end up anywhere and usually cause extensive circuit damage by shorting different parts of the camera. This is a Canon repair