Remote diagnosis is never easy, your photo doesn't really show much, and your description is a little hard to read (IMO mobile phones should be used for making calls and maybe looking at web sites, not for doing things that require typing).

However, it almost looks like someone connected that socket pigtail to the wires in the box and insulated the connections with masking tape! So, there's some chance that the connections were just loosely twisted, and the vibration from the sander loosened them just enough to open the circuit to the light.

Where you go from here depends on your electrical background. If you're comfortable working on this yourself, turn off the breaker to this branch circuit (not just the wall switch) before doing anything more. If you can't figure out which breaker it is, open the house main breaker and have someone hold a flashlight for you.

Remove the mounting straps so you can get into the box itself. Remove all the junk from the wires going to the socket and disconnect them from the wires in the box. Use pliers if necessary to straighten the bare copper ends of the wires in the box, then shine them up with sandpaper.

If you want to keep the old fixture, also clean up the wires of the pigtail coming from the socket. Usually it's easier to just cut off the bare ends and re-strip the insulation back about 1/2". A wire stripper from the hardware store will do the best job on this, but you can strip wires with a pocket knife if you're careful not to nick the wire itself or cut your fingers.

From the hardware store, get a small package of wirenuts. To get the right size, tell the counter person what wires you are connecting and how many. Probably you'll use orange or yellow, but colors vary, so ask.

Place the pigtail wire that's ribbed next to the white wire from the box, with the pigtail wire's end a little past the end of the white wire's bare part. Twist them clockwise (as you look at the end of the wires) and then screw on a wirenut good and tight. Do the same with the other pigtail wire and the black wire. If there's a bare or green wire from the light fixture, that should be connected similarly to the bare or green wire coming from the box (if any).

Make sure all the bare parts of the wires are inside the wirenuts and can't touch anything. Tuck the wirenuts back inside the box, put a bulb in, turn on the power, and try the light. If all is OK, replace the straps and reinstall the fixture.

If all this sounds too complicated, or if it still doesn't work, call an electrician. :)