iMac on the fritz! Frozen on start-up, installing update

I don't know why you're asking for my specs, I haven't worn glasses ever since I underwent Lasik. Anyway, I haven't been able to use this computer for months. It loads no further and furnishes itself with no use. I do not know what in tarnation to do! I've tried hitting it, dropping it from on high, and pouring liquid into USB ports; nothing seems to help. I can't even interfere with this window appearing on boot-up, no so-called "safe mode" is accessible.

'precciate any help.