I have erased a USB connected drive using Active@ Killdisk. Now the drive is not recognized by Windows anymore so I cannot format it. What to do?

Your disk is safe.

You can go to: Control Panel - Administrative Tools - Computer Management - Disk Management. The USB hard disk or USB Flash device should be listed there. You can right click on it to create a new partition and then format it.

How to use Disk Management to configure basic disks in Windows: Create and format a hard disk partition