There is a good chance the external drive is infected with malware that spreads using the AutoRun / AutoPlay functionality in Windows. Unfortunately there is usually a financial motive behind such malware - it can encrypt files on your system and then show you a message demanding payment for the restoration of your data - almost like a digital version of kidnapping. If your data is encrypted and you don't have a backup, the news is not good. If the malware is less sophisticated and all it has done is rename and change rights, there is still a chance of recovery, but you are going to need to find a VERY technically skilled (and patient) friend or company to assist you in recovering your data. You aren't going to learn these skills overnight if you don't already possess them.
The best option would be to entirely erase and reformat both your computer and your external drive, and restore from a clean backup. If you don't have a clean backup, you have probably lost your data permanently, I'm sorry to say.