Garbage characters display on PC bootup

I had a power supply that just “blew out” one day after plugging in the power cord, I saw a little smoke so I decide to remove the power cord and replace the power supply.
I hook up the power supply correctly and I when I press the power button thePC it boots up very well but on the monitor garbage characters are being display, but I can hear the hard drive and everything spinning as if working fine.The garbage characters apparently have replaced the normal characters as you can still make out “in form only” the energy symbol that comes up on startup(in color too). It is a Pentium 3 system. I don’t know where to start to diagnose this problem. Please help.Thank You!