I purchased a maytag dryer model mgd5700tq last nov i had the timer replaced in may now it isnt working again any ideas

Blower housing most likely stopped up with lint. This located behind front panel, lower section.

the heater element may of burnt through, or they may be a red reset switch on the rear of the dryer.

the part number you will need is 8566184 it cost about $80.00 dollars. from a local parts supplier

Normally if you have an automatic cycle that turns off the dryer when the clothes are dry, it will do it with a special thermostat or moisture-sensing system. The thermostat tells the dryer to heat until the interior of the dryer reaches a "pre-set" temperature.
When the dryer reaches the pre-set temperature, the thermostat tells the timer to begin advancing. If there is a moisture sensor, the timer advances only if the moisture content of the clothing is low enough. The timer advances until the interior cools, then the termostat tells the timer to stop advancing, and tells the dryer to start heating again. This cycle continues until the clothes are dry. But... if the vent is clogged, the dryer may never reach the proper operating temperature, so it doesn't send the signal to the timer and the dryer continues to run indefinitely, even if the clothes are completely dry. To fix this problem, clean the vent and/or internal ductwork and make sure the vent is not compressed or kinked. If that doesn't work, then your thermostat, moisture sensor or timer could be the culprit.
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Just had a similar problem with our Maytag Electric Dryer. The dryer shut off mid-cycle and wouldn't start again, but the timer kept running. We purchased a "Thermal fuse replacement kit" at a local appliance parts store for $38 and replaced the fuse ourselves. The dryer is running great! Here's a couple of website links that were helpful in figuring out out how to replace the fuse: http://www.partselect.com/repair.aspx?appliance=dryer&part=replace-thermal-fuse
http://www.davesrepair.com/DIYhelp/DIYthermalfuses.htm

Hope this helps!

The wire connections to the timer may have not been made correctly when it was replaced bypassing the OFF contact in the control circuit.  There should be a wiring diagram inside the front or back panel that you can check.

Call a local appliance shop and ask about it. Maytag is pretty common and available. The timer will be about 75 dollars. It could be more depending on what all you have on it. It is pretty easy to replace once you get to it. Let me know how this turns out.

Maytag Bravos 400 Series Dryer purchased August 2009 - November 2009 required repair as I also experience the timer readjusting itself to excessive extended drying time when clothing was bone dry and hot. Sometimes extended to 1 hour 40 minutes! Serviceman stated problem was the Sensors in the dryer. Part number 8577274 Thermister and "Old Ohmed out open" whatever that means as listed on my repair ticket. Have not had that particular problem since. Make sure your dryer vents from dryer to outside are clean and clear of lint. Will help immensely. I have many other issues with this dryer it has been down FOUR times in 9 months. Fighting with Maytag to replace this lemon!

hi please rate the last solution atleast as thanks for trying.

If the timer is not stopping as it goes around then it's for sure the timer. The timer does pretty much all the work with controlling the dryer. And if it's physically not stopping going around then it has broken.