Yeah you have to look at the negatives..
*If there is some evidence of frames but the image is very weak, the shutter fired but the shots are underexposed.
*If the frame squares are well defined but look blacked out then it is grossly overexposed.
*If there are long strips if just nothing, then the shutter did not fire or you left the lens cap on (it happens!)
The prints with the partial circles are probably mis-printed and you should be able to ask them to re-print manually. I've had this happen with fisheyes before.. the auto-frame of the machine gets confused. Again, you can always check the negatives for frame spacing.
You did not mention what verision you have but I did a quick search and it appears that the lomo fisheye has a fixed aperture of F8. it doesnt say what the shutter is but I bet it is fixed at like 1/30th. This means that indoors you are probably under-exposing 5 or more stops for iso 100 film (4 stops iso 200, 3 stops iso 100).. anyway, you get the idea.
So unless the lomo actually has slower speeds, you are using a flash, or very high speed film (iso 800+) you can pretty much rule out indoor photography.