symptoms for a toasted microcontroller?

Hi folks

I'm having a jolly time trying to make my three motors step in tune with my Arduino Mega 2560. Except for the problems finding and 'installing' a proper port, some timeouts of uploads and problems getting the serial monitor to work properly .. i did fair off ok, I think.
I thought that the current problem was 'as usual' .. that the port had disappeared .. but the device-icon has moved away from Ports and down to USB-Controllers where it's marked as an USB-unit that's not recognized.
I've tried to update, but the pc says, that the the unit already has the latest driver. Inspite of all the posts here on devices that's hard to get in contact with, I think that my problem differs. The ordinary trouble has caused me to do things that I would hate to do else .. pull the plug from the wall and such .. Each of the motors that is on the controller are powered on their own. Especially when I power the controller externally, one never knows where the current may flow .. if I let the system on it's own (no potential on motors ) it won't last long before led's here and there starts to light up.
Anyway .. whatever caused the current problem .. can any of you recognize the symptoms as a toasted controller? Or much better: recognize it as something I can do something about?

Kindly

Does the uC chip (the '2560) feel hot to the touch? That's usually a sign of one or more blown outputs and a chip that is or has failed.

Each of the motors that is on the controller are powered on their own. Especially when I power the controller externally, one never knows where the current may flow … if I let the system on it’s own (no potential on motors ) it won’t last long before led’s here and there starts to light up.

A schematic may help here.

"Does the uC chip (the '2560) feel hot to the touch? That's usually a sign of one or more blown outputs and a chip that is or has failed."

No .. there has been no obvious signs.
The (12v) steppers I use is another matter but they shouldn't spill over to a degree that it spoils the controller. The steppers came to work properly when I added some 3 ohm resistors. I havn't got the proper tools, so I soldered 3 1-ohms together in series, and at some time on testing the soldering melted.
I've tested and continoually checked the motor-drivers for overheating - but they've been extremely fine compared to without the resistors. I checked the Mega-controller once, but it wasn't warm in any way. The work is on the motor-controllers. The testings has been less than a minute at a time.
I do, for the time being, control the Mega through the uarte .. and the loaded code is tuned to that. I will have some manual controle at first convinience.

Florinc,
I don't have a scematic. In the standard-testing the Mega controller is just powered through the port and no problem. The setup is straight-forward with 3 stepper-drivers (dual h-bridges) with each 6 pins hooked up on the Mega. Since the motors behaved better than previous I was quit jolly, but I could not seem to use the serial Monitor which was needed to start/stop .. I think that it got blocked by 'return-values', but it made me jumpy and I would shut all down in a non-standard way (hate to do that) .. It's a bit tin to spoil the Mega, but it's no longer recognized by the pc. I did recognize something unusual that happened on the pc (something about 'could not delete temp file' or something unexpected that had nothing to do with anything).

Carsten

/I'm not good at sending these .. so it may pop up twice/

EDIT
Did reinstall the win7 on asus 64bit .. and even brought my old 32bit winXP-pc back from the dead on a clean hd .. and all for no vail. The situation has not changed one bit. Pop me a suggestion, please. Is it a one-way street to 'change' a controller? It looks quite new (and 'is'), but it could just as well be burned into a sinder as it is.

EDIT I read on the "Arduino Mega 2560" that:
quote
SPI: 50 (MISO), 51 (MOSI), 52 (SCK), 53 (SS). These pins support SPI communication using the SPI library. .... . The MAX3421E comunicate with Arduino with the SPI bus. So it uses the following pins:
Digital: 7 (RST), 50 (MISO), 51 (MOSI), 52 (SCK).
end Quote

I have used pins 50 & 52 for one of the motor-controllers (i1 & i3) ... could this be a source of error?