using HTC Google Nexus One, Android 2.3.4

This is very strange, but I noticed today that my camera is no longer working. I have no idea why, but it just goes black when I select camera. I have restarted my phone, took out the battery, etc. and nothing. Also, I even tried downloading other camera apps, and they won't work either.

Even more frustrating, though, is that my phone goes black when I make or receive a call. The calls do not get dropped, but when the call is over, I can't even hang up, as my screen is black. It's weird because my phone is still "ON," but I obviously can't do anything. The only thing I can do is take out the battery, put it back in, and turn the phone back on. Then, it works perfectly normal...until I make or receive another call. I have no idea what to do.

Can anyone help? I'd really appreciate it, as I use my phone for everything!