I change the belt and now, I have a new problem. The cassette won't go inside the vcr. When I push the cassette, the motor won't start. If I shutdown and shuton the vcr, the cassette goes in and come out immidiately.

Your Mitsubishi VCR HS-U580 looks to have a problem with the information rollers and drum. Here are some things to check:
Look for something blocking the VCR or cassette compartment that would possibly be stopping the guide rollers.
Check the belt that drives the VCR mechanism. If it is loose or broken, you may also need to substitute it.
Clean the video heads using a head-cleaning cassette to make certain they're not dirty.
See if the drum motor is working. If it is not spinning, there may be an issue with the motor.
If the trouble persists, it's an exact idea to get assistance from a professional technician or contact Mitsubishi's purchaser support for advice.
Be cautious when dealing with electronic devices, and if you are not certain what to do, it's great to get assistance from an expert.

I forget exactly how this goes but there are two posts on either side of the mechanism that read a light signal and a center pole that goes through the round hole on the cassette that gives the light signal (no tape-end of tape). Put a piece of tape on the two side posts and see if that changes anything. Be careful: the tape now knows where end of tape is - do not fast wind/rewind to the end! The loading motor may have failed or a rubber belt has slipped off or is too loose or broken.

Units that sit do not exercise the belts and this causes some belts to become deformed and then other to just decay to like a tar. Look inside the unit to see if the motors are turning. If they are you will see it needs new belts. If the motors are not turning then the likely cause is Electrolytic Filter capacitors in the power supply. They don't do well sitting either.

the tape coming back out and unravels the tape means the loading mechanism is the problem----when a tape goes in it loads the tape down, then it pulls the tape out of the cassette and puts it up against the drum with the video heads-----many of these are belt driven and a bad belt or belts will cause this----it is called the loading and or transport mechanism.......when it fails the arms come back but the tape does not get rewound back into the cassette so it mangles it when the cassette door on the tape closes----most likely a belt or the drive idler which also rewinds and fast forwards the tape.

The tray needs a new motor with a new pulley that does not slip on its shaft and get a new belt too.
It is easy to pull the dvd tray unit out of a GO VIDEO DVD+VCR machine to replace the motor with new pulley on it and the belt should be renewed too.The motor NOW may run only to push out the tray but it will not pull it in to LOAD the DVD or CD.
This is what I found after troble-shooting the function.
From Jim, and I need the same things. Can anyone tell me where I might buy those idems? [email protected]

Hello
There si one belt connected to its capstan motor to reel drive gear assembly to reel up the tape. If this belt has either loose or broken, the fault you described here will occur. To change the belt, you have to buy one new with same diamentions. To get it, you must ahve the damaged belt in hand as sample. Just look at its bottom side, and is there any extra sid screwed into, which can be removed to see and take the belt away from the mechanis. There will be one, with every Toshiba VCR. If so, open it by unscrewing the screws, take out the belt, buy a new one and replace it.
Before doing this, make sure that the capstan motor is rotating or not. Just unplug the VCR from power socket, and replug it again. If capstan motor try to rotate even a single turn, it means that it is OK. Replacing the belt should solve your problem.
If you want anymore asistance, feel free to get me through Fixya. OK.

turn on the machine. use your figure push on the cassette, when you feel the cassette can't go any farther (don't jam it),and hold it there. press the eject button, you may have to try this couple of times in order for the cassette to come out.
the cassette deck need to have the drive belt change.

Open bottom metal cover. Rotate the belts of the motor. Cassete should unload from Spindle and reel back into the cassette. Then please open the VCR top, and you will see a belt and gearmechanism on the right side of the cassette compartment. Manually rotate the gears and the tape will slowly come out.

Firstly: do not think about forcing the cassette door! Look inside the unit. You need to hand rotate the capstan flywheel a bit,( a large-ish metal disc attached to the motor via a rubber drive belt.)That should release the powered deck mechanism and allow ejection. Then buy a new drive belt , so that problem does not recurr. Good Luck