Star-up disk Full; cannot start my 2008 iMac w/ 500 GB hard drive

Kept erasing empty files from my early 2008 Intel iMac(with 500 GB hard drive). Kept getitng message 'Strt-up disk almost full.'

Used Hard drive as start-up disk. Kept getting a file labeled (approx.) EFileS1...(didn't write it down). Tried once to totally erase

this file: Removed Garage Band by moving to trash and securely erasing; and other files( 1-3 Mb at most. Now, get message "Start-up disk Full" and I can't

log onwhen I enter name and PW, I get the screen saver; I don't get the dock or anything else. I tried to use a external hard drive, and I also tried using an external CD/DVD player (integrated one no longer works) to reload SnowLeopard (OS 10.6) with no response (I had upgraded to OS 10.6.8).

I'm now using a Nov 2008 MacBook (burned out screen with external monitor) to write this email).

I'm going to buy 2014 MacBook Pro 15in w/ retina display as my sole computer, but my iMac hard drive has documents I'd like to save-Then I plan to totally

erase its HD before discarding/donating.

All suggestions and help will be appreciated.

Snboshu