I bought an 800 on EBay for $250 for my 750. Would do it again!
When in transit and don't have time to monkey with settings leave camera in auto and you will get a respectable shot. If you need to force a flash - turn to 'P'.
My 750 did this also right after I bought it, about nine months ago. Reboot remedy - same as what you did worked for me also. Has not happened since. I did do firmware upgrade about six months ago.