I changed a portion of galvanized 3/4' pipe to pex tubing. All was fine for awhile the suddenly the cold water stopped running in portions of the house. Should I call a plumber to get him to blow out the rust and debris? Or is there a simpler method I can use on my own?

Galvanized is known for getting deposits on the inside and breaking off when cutting it. I would first remove all faucet aerators and open the CW faucets up. Clean the aerators and reinstall. If that doesn't fix, you may have debris in the angle stops.

Good call Brian. If the aerator didn't get it then try this. Try this. Shut the water off to one of the taps and pull the cartridge, Check the inlet ports for trash and clean. Now place a pan over the open valve and turn the cold water back on for a minute to flush out the supply. You should have a strong stream when doing so. Reassemble and test. If that works do it on all affected taps, good luck, Tom