I have an Ascer Aspire M5641 AM5641 desktop. While looking at video online, the screen went black. Everything was still on and runnimg but I could not see anything. Thinking it was the monitor, I replace it. It wan't. The way the screen went dark, I guessing now, it must be the video card. I therefor need a new motherboard. Can you help in what kind that would match and fit?

SOURCE: Acer desktop mouse,keyboard not functioning, monitor also not wor

If there is no display on the monitor, then your computer is not sending a video signal to the monitor.
This could be caused by a bad video card or some other hardware problem. I would open the case and disconnect all the devices (hard drive, CD, etc. Leave only the CPU, memory, and video connected. You could leave the keyboard and mouse connected too.
If your computer then starts, you can start to add devices (after turning the computer off) one at a time.
If this doesn't work, then you are looking at replacing the motherboard or just the video card if that is possible.

SOURCE: Acer AM5641-U5520A will not

If you removed the memory modules and there is no change then I would start disconnecting one device at a time to see if that is causing the problem. Start by disconnecting the cd/dvd rom and then try booting the computer. Then try disconnecting any floppy drives or pci cards(except for video card). If it has a pci/agp video card then you will need to remove it and test it in another computer or test a working one in the problem computer. If it has built-in video then you will need to test a working video card in the problem computer. It could also be an issue with the power supply so remove it and test it in another computer or swap it out with a known working power supply. Also check the mother board screws that hold the board to the chassi are tight(the board uses them as a ground). Blow any dust out of the case and verify that there are no loose connectors. Also verify that the monitor is not the problem by testing it with another computer. Usually when a CPU is defective the computer will not respond to anything and will act "dead" so it does not sound like the CPU. If everything else checks out then it could be a bad motherboard.

SOURCE: Aspire AM5641-U5520A PC Desktop knowledgebase ...

Try installing new memory

SOURCE: I need to know what motherboard to replace the

Gigabyte, Asus, MSI etc, the choice is yours.

SOURCE: My Acer Aspire M5641 freezes

The video hardware is heating up and triggering a thermal sensor, or it's failing due to excessive heat. You might try running air conditioning when you want to play the game that freezes the computer.