1999 Ford F-150 engine died and wont start

Engine made no attemt to start when key was turned, jumped solenoid and started fine and would start normally for a while. Sometimes it would start simply by moving the gear shift lever a little while starting and other times would have to jump solenoid. Replaced solenoid and still had the occasssional problem. Two days ago lost power to radio and windows while driving and would not start again. I was at wal-mart so had them look at batterty and was told that it had a bad cell. They replaced battery and it worked fine until today. Radio starting cutting out and windows operated very slowly so I left engine running and left vechicle for 5 minutes. When I returned engine was no longer running and it would not start, it would just click when key was turned. Tried again 10 minutes later and it started. Drove to office and just made it when I lost electrical to interior and engine stopped running again. Has not started since. Sometime when key is turned the interior electrical wil work but fluctuate. Total silence when I try to start it up. Where should I start looking at problem.