I am new to Digital Photography and so here goes. I started using an inexpensive Bower SFD728 Canon compatible flash and after successfully taking several still shots with my Canon rebel 400d XTi, on the P mode, the images began coming out white,(could see outline of image faintly) although the flash triggers. The built-in flash works fine. Took over 300 shots perfectly before problem arose. Then, by accident, I pressed the FE Lock (*) and the shot came out fine. However, this has to be activated for each shot. I am puzzled, to say the least.
Not sure what the problem is. Help please.

