Check all of the valves to make sure they are all open. A partially closed or closed valve will reduce the water the sprinklers, causing them to not properly pop-up. Many electric solenoid valves used to operate the sprinkler zones have a flow control handle/knob/screw on them that allows the valve to be manualy closed or opened.
If your valves have a flow control, check and make sure they are completely open. Turn the handle counter-clockwise to open it. If water starts coming out, stop turning it and retighen it!
Try manually opening the electric solenoid valve. There should be a lever or snall bleed screw on the valve that allows you to bypass the solenoid and open the valve. (Additional information can be found in your owner's manual). If there is a bleed screw, open the screw until a small stream of water comes out, but do not remove the screw completely, it is very hard to get back on if you do. If the heads pop-up fully when the valve is manually opened then the problem is inside the valve
Turn on a single valve that has heads that will not pop up. Sometimes a grain of sand will wedge in the gap between the riser and the cap of the sprinkler, causing the riser to jam. Press the pop-up riser down firmly with your foot, so that it is pushed all the way back down into the body. Then release it so it pops up again. Repeat this step about 4-5 times to loosen and flush out any sand grains.
Check for excessive blow-by of the sprinkler riser. When the riser comes up, a small amount of water squirts out of the gap between the riser and the cap. This is called Blow-by. A small amount is normal to have.
To check the blow-by, have someone turn the sprinkler valve on while you watch the riser on the sprinkler as it pops up. To determine what is normal, compare several sprinklers, check to see which one(s) squirt more water than the others. If the sprinklers have excessive blow-by they should be replaced. Make sure you use the same brand and model for replacements.
There should not be any water leakage between the cap and the riser when the riser is fully extended. Turn on the sprinklers and check for leakage on each one. The riser should be fully extended. If the riser does not come up all the way, pull it up with your hand. If you find leakage between the riser and cap when the riser is completely up, then either the riser seal is bad, the riser is scratched, or the cap is scratched. You should replace the sprinkler is this is the case.