Usb connected constantly flashing on screen
Your usb port is bad - this is a hardware issue. Take the phone in for warranty service.

Edit: I had this happen on my Nexus S as it came out of the box today. I flashed the latest stock ROM, then re-installed CyanogenMod over top (and restored my data). It seems to be a little less flaky. You may not be able to do anything of the sort, but it may help others.