Replaced timer less than a month ago, now washing machine will only fill, then stop. What could it be?

The wire coming from the water level switch is either in the wrong place or missing, or the water level switch is bad. You need to check the water level switch with a meter. It has a common (where power comes in), a normally closed to water valves, and a normally open to timer. If you want to fix it you will have to get a good digital multimeter, or even an analog meter, but a digital is better if you have never used a meter. Here are the manuals you will need: https://dl.dropboxusercontent.com/u/...c%20washer.pdf (https://dl.dropboxusercontent.com/u/8010163/Understanding%20automatic%20washer.pdf)
https://dl.dropboxusercontent.com/u/...e%20Manual.pdf (https://dl.dropboxusercontent.com/u/8010163/How%20to%20use%20Test%20Equipment%20Service%20Manu al.pdf)
https://dl.dropboxusercontent.com/u/...%20washers.zip (https://dl.dropboxusercontent.com/u/8010163/Whirlpool-Kenmore%20washers.zip)
This is good, too:https://dl.dropboxusercontent.com/u/...Electronic.pdf (https://dl.dropboxusercontent.com/u/8010163/How%20to%20Diagnose%20and%20Fix%20Everything%20Ele ctronic.pdf)
Go to Home Depot, Lowe's, or (expensive, but good) Radio Shack and find a good digital multimeter. A good meter will have automatic voltage protection in case you have voltage on a circuit when you have it set to "ohms." Make sure to ask about this feature. Others will have a fuse to protect the meter in case you have voltage on something, like a capacitor when you have it set to "ohms." On your washing machine there are three things that control water and start the wash cycle: The timer, the water level control, and the water valves. The water level switch has a plastic hose that goes to the bottom of the tub and to a diaphragm on the switch which operates a switch that has a common (incoming power) that is normally closed to send power to water valves. When pressure is applied through hose (You can blow on hose to test it.) the switch switches power from the water valves and sends it to a switch in timer to send it where it is needed. When you blow on the end of hose where you pull it off the tub (Pump out water in tub first and unplug power.) you should hear a click. The switch will then open the normally closed connection to the water valves (unplug wires to test) and close the one to the timer. If it's not closing the one to the timer then it's bad. If you are replacing the timer without knowing for sure that it was bad then your problem was probably this switch all along. You can test all of this in a few minutes with a meter. No one can guess what is wrong; they can only tell you how to test it, and anyone who does it any other way is doing things wrong. You test first and then replace parts, not the other way around. When you are through testing you may want to trim off each end of the plastic hose so you get a good tight fit on the water control switch.