|If all you did was change the battery then I'd assume you cleared cmos. That may mean that the default settings have returned. If you had a built in video port then the default goes to that.|
I'd remove ac power, press power button a few times. Use esd strap and remove cmos battery for a bit and carefully return it. Be sure polarity is correct. Look for any connection that may have been bumped in the process and re-seat it. Power it up.
Any fans or keyboard lights or other indications of how far it is getting?
1/3 of highway deaths are caused by drunks. The rest are by people who can't drive any better than a drunk.