It's probably safe to have the external drive connected. The following links are not your exact problem but you can see what happens when a person connects another drive while in hibernation. Hibernation dumps RAM to disk so there may be a chance of corruption. That's why I do not do it, especially when a USB flash drive is attached.
With the USB flash drive attached is there anything in Disk Management? Is it listed as RAW? If you see your drive, partition and format it in Device Manager. If Disk Management does not see the USB flash drive, there may be a chance linux can find it. Download Puppy Linux. The lupu-528.005.iso is a good one for old computers. Burn the iso and boot. After Puppy loads to the desktop, attach the USB flash drive. You should see a USB icon appear in the left corner. Run Gparted from the Puppy Menu. In the upper right is a dropdown box. Make sure you are selecting your 8GB flash drive and not your internal hard drive. Select it and select Device > Create New Partition Table in the menu bar. Then partition and format it to FAT32.
Here is a good tutorial on it's use.