The belt on my ProForm Crosstrainer treadmill stops while using i

fuse,reset,or overload protection

see the video and fix it. Lube too the rollers bearing front and rear+test the drive belt motor and replace if necessary. tight a little.
God bless you

Walking Belt is Worn: The only certain way to test for a worn walking belt is to take a DC amp draw (if you have a DC treadmill) or an AC draw (for AC). Trying to look at the belt or a feel test is highly unreliable. Better tests, if you lack a DC ammeter (they are expensive for a good one), are a coast test or an incline test. The coast test is to get on the treadmill as the lowest incline setting and walk on the treadmill at 3 MPH. Pull the safety key and it should take you 2-3 full steps to stop (this is a general rule…some like a few Tunturi models stop on a dime even with a healthy belt but for most models, this tests works well upon). Fewer steps indicate high friction. The incline test is to put the treadmill at max incline and walk on it at 3 MPH. If the treadmill operates normally at max incline but bogs down at minimum incline, replace the walking belt. Gravity takes over for the drive system eliminating much of the friction problem. On some heavily worn walking belts, this test will not eliminate the problem. Go to your local hard ware store and purchase silicone spray. Apply Lubricant by lift one side of the running belt spray contents length wise starting at motor shroud to the back end repeat this process on the other side. If this unit bogs down again then you will have replace the running belt and possibly the deck

take the cover off, if the front drive roller continues to turn when the running belt stops, tension the running belt by using the rear adjustment screws. One full turn on each side should do it. If the front roller stops turning but the motor doesn't, tension the drive belt by adjusting the motor back.

HAS A SHORTED MOTOR CONTROL BOARD NEED TO BE REPLACED.
GO TO iconfitness.com then to customer service then parts repalcement

look for a tension knob it will tighten the belt unless the belt is really wore out and may need replaced

Most likely a bad drive belt. Take the cover off the motor area. If you see black dust near the left side of the motor, replace the drive belt.

Your belt may need adjustment. to tighten you need to use the allen key (supplied with the unit)

Belt needs tensioning up on its adjusters or the motor drive gear has come loose and needs tightening back up.

Check both belts to be sure they are adjusted and not slipping.Check the underside of the walk belt to see if it feels frayed in the center as compared to the edges, the center always wears more than the edges a really worn belt must be replaced. if it is nor worn there is a wax lubricant for proform treadmills that can be purchased at retail stores that sell treadmills.Sears, dicks sporting goods and also treadmilldoctor.com are good places to buy it.