Fresh battery is a good idea. I'd check that first.
However, if you can get the meter to work (press the shutter button, or the button on the front of the camera), then it may not be the battery.

I've a Sears KS-2. These are basically rebranded Ricoh cameras. I've not had the mirror lock up, but have had the shutter stick.

You could try putting your finger on the edge of the mirror and pulling down gently. However, if it is related to the shutter being stuck there may be something to investigate.

The foam seals degrade with age, both on the mirror, and on the back. It only takes a tiny bit of this to get in the shutter and make it stick. First examine the back door open and see how the foam looks on the door edge where the hinge is, and in the camera body grooves (horizontal) where the door seals. See the foam is intact.

When I've had the shutter stick, I was not able to see the sticky bits. I had to let the camera sit for a day or so while it "dried" a tiny bit and the tension already present helped free it. I gently worked the shutter curtains and finally got it to open. After I cleaned out the foam residue from the back and grooves, replacing it with wool yarn and felt, I've not had this problem.

I'm only guessing that this is related to the mirror being stuck. Also, the foam on the mirror may also be sticky, causing it to stick to the top of the mirror box.