Not turning on at all

I have read substantially to ID the problem. Camera died while shooting, replaced the battery with a fully charged one. Within minutes it died again and showed an error code briefly when turned back on. Then would not turn on again. Have checked CF door and removed CF card. Tried it without lense on. Open up the bottom and found the loose screw (common problem) and put the crew back. Yet still as dead as a doornail. Please help.