Things to do :
1) disconnect the drive from the USB port. Wait a few minutes. Reconnect. If possible, use another USB port.
2) Power the drive off. Wait a few minutes. Power on.
It is unlikely, but not impossible, that the cable is faulty. Unless the cable show some obvious damage, it's probably not the cause of the problem.
As it fails to be recognized by two different computers, it may be an hardware failure of the drive or it's enclosure.
In that case, look if you can take the drive and place it in another external enclosure.
If it don't work in another enclosure, you have a drive failure. Assume that all the data it contains are lost.
Get some disk diagnostic application. Be careful as there are fake ones. If a free utility offers to scan for free, but demand you to pay something in order to repair things, then +, you have a fake, scam, application.
Some times, those can repair a critical sector that went bad.
If you can now access the content, you must IMMEDIATELY copy all of it to somewhere else as that drive is no longer reliable and may totally, and irrevocably die.