Camera Won't Turn On

I bought a used Powershot S3 IS, and I can't get it to turn on.

Things I've tried so far:

• New batteries (AA and coin cell, using 2 different brand-new sets)
• Cleaning the batteries and contacts with rubbing alcohol
• Checked the little buttons in the battery and SD card areas, the ones that get pressed down when the lids are shut (they both seemed to press down fine)

It still won't turn on, and there are no sounds or lights when I turn the power knob. Also, I don't know if it's supposed to be like this or not when turned off, but I can't see anything through the viewfinder - just blackness.

If you can think of anything else I could try to get it to work, I'd be very grateful!

It didn’t cost very much, so it's not the end of the world if I can't get it to turn on, but I'm still hoping I can get it to work.