mac makes beeps and won't allow keyboard entry

imac with OS Yosemite, 4gb. Was working fine when I shut down yesterday but upon bootup today I hear a continuing beep (maybe not the best description) or intermittent sound whenever I try to enter keystrokes in a browser. In addition, a series of double dashes (see attached) runs across the search window, as if a key was 'stuck' I detached my keyboard, but it still happens.

In effect, my imac has been 'hijacked' as I cannot do anything. I checked e mail but when I tried to send a msg, the automatic string of dashes fills the screen until I close the e mail.

I restarted and also tried booting in safe mode, but the problem persists so I can not run any utility to try to solve the problem. I did look at my directory and noticed that a file with a name something like zebrouss (?) was there, which as I recall was a type of malware...and wonder if that might be a source of my problem. HELP!