try to consult your service center. there are two possible reason:
1. check if there is sometthing blocking the mirror. in some DSLR there is a latch inside if the mirror does't reach that latch it will return back. the same with a DVD ROM if you block the CD tray it will return back.
2. another reason is the firmware might have an error or bug. in canon you will just update the firmware. I'm not sure with olympus.
please consider switching to nikon, panasonic, canon or Sony because there are a lot of people that might help you or there are many parts available if you want it to be repaired. I'm not saying olympus is a bad camera.
but try to do this