I've had my N75 for about 5 months and it has been much tougher and more durable that I believed. I underestimated the N75 in many ways and I love finding new ways that I have. HOWEVER. For the past 36-45 hours the larger internal display has been dark except for a faint glow when viewed from an angle. I am able to make and receive calls and text messages using a series of key strokes that I must have memorized at one point. Tried variations of powering down and backup, no results. Chatted on the at&t tech support forum and they recommended a Master Reset of the device. I have attempted this but my keystroke memory fails at this because it is clear that the phone hasn't reset because it didn't automatically boot.
yeah, i cracked the LCD on mine when i dropped the phone with the fold open. Sounds like you need to send it in to Nokia and have it looked at. It cost me $105 to have my main display LCD replaced and shipped back to me.
If the screen isn't cracked you can just do a warranty exchange by mail and get it replaced for free. If it is cracked, then I'd use your phone insurance if you've got it or, if you don't, then contact nokia as the other person responded. $105 is kinda steep but it beats what you'd pay for a new phone.