Still getting EFI error tones after replacing PRAM battery

Mac Mini mid-2010 used it for about a 18 mo no problems, then put it on a shelf. 3 years later, it won't start... the SOS error tones sound. I put it back on the shelf for a year.

Today I replaced the PRAM battery, after numerous references to this, as well as swapping the RAM cards (with each other) and dusting them off.

Still the beeping tones, can't do safe start up, can't reset SMC or PRAM.

Anything else I should try before I sell this thing on ebay for parts?