Try forcing water into the intake tube with the pump running; a turkey baster or nose/ear bulb works well. If the pump still will not suck water on it's own it may be partially plugged with calcium, if you haven't been regularly descaling. Seattle Coffee Gear can repair these machines and gives free repair estimates.
"We tried everything to unclog the water line. We used a turkey injector a couple of times and it pushed whatever was clogged thru, and now it is working great. We were going to try the turkey baster, but the end was too big to fit in the hose.
I didn't know to use a descaler, but will buy some and use it frequently now."