A problem with invisible text! Strange setting? Glitch?

Hi, I'm not exactly a beginner at Photoshop 6.0 but I'm self taught. I was adding in some text to a hand drawn image that I scanned in. I put in the first label and it was going smoothly, then I highlighted it and changed the font and the black lettering I put in disappeared.

It still seems to be there, and it shows up in the Layers box. It's just as though the opacity has been turned down to 0% (which it hasn't). It's not stuck behind another layer and it's not the same colour as the background. I can still copy/paste text in and out but I can't make the text visible. Even if I put a colour overlay using the Layer/Layer Styles/Blending Options, it still won't show up.

Even if I start a new image, the same thing happens when I try and put new text in. Basically, my ability to add text to an image has been totally incapacitated.

Can anyone tell me what's going on? Have I leant on the keyboard and triggered a short cut I didn't know about? Is it a glitch or a screw up with the program. Anyone else encountered this, and can anyone fix it?

Cheers.

welcome, eds!
What is the blending mode of the text? what is its size? what is the resolution of the file? are you sure that the font has the characters you typed? have you tried other fonts?
are the questions that you should answer to try to find the solution of your problem...