Although the watch is IP67 certified, that does not mean the watch is certified for diving. IP67 means that the watch is certified waterproof down to a depth of 1 meter (approximately 3 feet). This means that the waterproof seal may have failed and damaged internal components while you were diving. Check inside the watch - on the inside there is a small circle attached to the inside of the watch, near the battery. This circle turns pink when water has entered the device. If you see water, or the circle is pink, then water has entered your device and may have damaged internal components, such as the motherboard, which would cause your watch to no longer work.