Mirror is locked open

if its just a sticky mirror you could try to very genteely flip it down again but if the shutter is jamed in its sliders it could need to go to a camera shop to get it "fully serviced!" also check its not just the shutter lock button stuck in, or the shutter is locked open,

Mirror lockup often occurs if the batteries are flat.

Try new batteries first and if the problem remains please report back for further options.

Does the film advance lever lock in place when the lever is returned ? if not, the lock spring broke. This is a common weak point in the ME Super. the camera must be partially disassembled to be repaired. get a cost estimate first. there are no new parts for this model Pentax.

It doesn't need batteries to shoot. You can use it on manual without batteries, but the exposure meter won't work (if you know what you're doing you can go by). But the stuck mirror should be fixed. It could be just plain dirty/rusty/bent etc.
The advance lever might be gone since it won't 'click'. A professional shop can fix it, but the one you tried doesn't sound very professional...

if the re-wind button is not stuck in, then the tab on the advance shaft is broken off. this small piece of metal will jamb the gears eventually.
take or send your camera to a repair shop for a cost estimate before repair as there are no new parts available for this model .

Pentax ME Super was one of my favorite camera, small and clean shutter release. But it has been about 25 years since it was manufactured. They happen to use rubber break within shutter unit and as any rubbers, it started to deteriorate and melt between the shutter-blades. This prevents the complete cycle of the shutter and jams the winding. You may be able to unjam the winding but eventually you have to overhaul the shutter unit. Overhaul charge is around $100 in US repair market. -James

anmolag,

it could be the rubber bumper next to the fresnel lens has become sticky. very gently ( after removing lens ) try to bring mirror down without forcing it. it should release easily.
if not, rotate the select knob off auto. open film door and check that the shutter is fully deployed, shutters should not be overlapping.
remove screws from bottom cover and remove cover, keep camera up side down so that re-wind button stays put. there is a locking lever under the take up spool ( gray ) . with a pin move lever toward film door and bring advance lever fully to the right , then let it go so it returns quickly.
the shutter should have fired. if not the camera will need to be repaired. get an estimate first as there are no new parts available.

The problem is actually the mirror box controlling mechanism and not the shutter it self ,strictly speaking. What is happening is that the locking /unlocking of mirror, when it is cocked, is gummed up by perished rubber bushings and rubber shock dumpers ( life span of 15-20 years max ) .
You need to get to the left hand side of the mirror box ( easy to locate once you take the m. box out ) and clean out with isopropanol ( can use benzine but is unhealthy ). Relatively easy but make a note of where the wiring goes ( shutter and l. meter ). And then also take care with the mirror box -cocking mechanism at the bottom ( draw picture of position before dismantling ).

Your camera is cocked but since the shutter is not working you cannot release it and hence your film advance mechanism does not work. ME-super will work without batteries in full manual mode so set your shutter to B and try to release it. If the shutter will not release in B mode then the shutter/mirror box will need servicing : rubber components in the mirror box mechanism have perished and need replacing. After that your camera will be fine for another couple of years.

Yes this is fairly common with K 1000 and the Spotmatics : although the shutter is cocked and hence you cannot advance film you cannot release shutter because mirror box is not cocked. Remedy : remove bottom cover and locate mirror box lever which protrudes slightely and is movable up and down and is spring loaded. Move upwards until it licks in position ( moving up against spring tension ). Now release the shutter and camera should let you advance the film .