It sounds like the boot sectors are damaged (may even be a malware infection)
I assume you have a Windows system here:
Do you have a friend that has a Mac?
What you need here is to use a disk utility that won't alter the drive to a Mac readable drive but one that can fix the boot sectors for your Windows based drive, not many Mac utilities offer this. I would recommend your friend to get Drive Genius. If at all possible run a good antivirus program (with the latest def files) on the Mac on the drive before trying the drive back on your Windows system. Also check your Windows system fully in case it has something on it.
You could also try Linux and run on the drive repair & antivirus tools available with it as well.
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