Can you see the drive in Computer? If so, Right click on it and choose 'Properties' On the 'tools' tab under Error Checking choose 'Check now' and tick the box 'Automatically fix' etc. If it can't check the drive as it's in use allow a dismount or check when you restart Windows.
If that fails
Right-click "My Computer"
Select "Manage"/ "Disk Management"
Expand to full screen
Look for your Ext drive in the right pane.
If shown, right-click in the area showing that drive.
Click "make drive active" if you have the option.