What did you do?Reinstall?Is the system running OK now?
When was the last time you ran this spare box?Did you fire it up with the existing OS before you installed Linux?
If it still does that, just how far into the boot process does it go?You should see a couple pages worth of messages scroll down the screen before you get a login,wether it's a CLI login or GUI login.
Are you seeing any error messages before the screen goes blank?
When you say the monitor acts like there is no signal going to it,do you mean it stays blank and the indicator light turns yellow like it's in power-saving mode,or does the light stay green?
A couple more things that may help narrow this down:when you installed Red Hat,did you get a full-blown GUI installer or a text-based menu -style installer?And did it offer you the chance to configure and test Xwindows?I seem to recall (from RH 7.3) that RH does the X configuration pretty early in the installation process.
Sorry for all the questions but it will help to know the answers
HTH
lynch