Have you checked to see if your memory card is full? The camera should notify you if there is no more available space to save photos and videos. In order to manually check remaining storage space, go to Settings->Memory. This should display the remaining amount of memory. If it displays a size lower than a few megabytes, you will need to transfer some pictures to your computer to free up space, or buy a new SD card. If you have any other problems, please consult the troubleshooting page.

Unfortunately, the flash mode is not available when in video mode, only in Auto scene modes. As for switching back to Auto mode to test the flash, your battery may have been too low to function. The flash needs an ample amount of battery in order to work, so try recharging your P90's battery. Here is the troubleshooting page for any other problems you may encounter.