These units seem to be suffering from a bad connection on the inside of the unit. My wife's did the same thing. There was a connection inside that wasn't making contact. First try cleaning the 4 brass connection tabs on the watch and check your charger to make sure the tabs are raised and not squished. Second try to reset the unit. Hit mode reset and power buttons all at the same time. Hold these for 3 seconds and then release. If these do not work here is what I did. There are no screws holding the unit together. I used a exacto blade to very carefully pry the unit apart along the side seam. It's not easy to do. Be very cautious and gentle. Work the thickness of the blade into the joint to gently wedge apart. You are not trying to remove material! Once apart you will see some fingers that make a connection between the upper and lower part of the unit. This is where the problem was with my wife's 305. I gently raised these tabs to make a better connection, It's been working ever since. I didn't try it before but try pressing very hard on the unit where it says Forerunner 305. The case is very hard so it might not work. But if it powers up when pushing you found your problem. Hope this helps. Here is a link I found on opening a 205 (Same process) http://ctorunner.googlepages.com/dismantleforerunner205 To put the unit back together use Automotive silicon/gasket maker. Use a tooth pick to put a VERY small amount of silicon around the entire seam. Put the two half's together and wrap tightly with electrical tape. Test the unit immediately to see if it powers on and off. If it does not open it back up and raise the small prongs that make the connection from the bottom half to the top half. If any silicon squishes out the sides wipe with water and a rag. Let the unit sit over night. In the morning remove the tape.

Let me kinow if this helps.