Check to see if the power supply to your dishwasher has been cut. Your machine may have been turned off mid-cycle, been unplugged, tripped your breaker or blown a fuse. Make sure power is getting to your dishwasher before continuing to troubleshoot.
Consult your dishwasher's user manual for instructions on how to reset it. The method for doing so will depend on the model you're using. Resetting your machine will interrupt its current cycle and return it to its prewash status.
Turn the machine off and check your its water inlet pipes and drainage system. Some Bosch dishwashers display an error code if they experience problems with their water supply or waste disposal filter. Make sure your water inlet pipes are properly connected and are receiving a good flow of water and check that your drainage tube is not blocked.
More recent dishwashers from Bosch come with a childproof locking system that disables the door from opening unless it's deactivated. The method for operating this depends on the model of washer you own. Check your unit's documentation for information on how to deactivate your childproof lock.