When you move a hard drive from one system to another.
Say your laptop to the usb drive enclosure.
Two things can happen.
First of all because the drive was used and formatted via a different interface mode say Sata.
And then swapped over to a usb interface it can render the drive not being able to be read by windows due to the interface change.
The second problem you need to take note of is the existing drive letters of hard drives in the dell desktop.
If the drive you are placing in the usb enclosure has the same drive letter assignment of any existing drive of the desktop system you will be asked to format the usb drive due to that conflict.
To get around it use disk management of windows.
Click on the action tab, and then rescan drives.
Go down the drive listing, till you find the usb drive.
Look at the left most side to see what the status of the drive is.
If it does not say Online.
Right click on the next window payne and select change drive letter or path.
You need to select a drive letter for the drive where not other drive is already assigned to it in windows.
So pick J: or K: for example then apply the changes.
After that check the status of the drive. and set it to online via right clicking on the first window.
If successful, restart windows. and you should have access to the drive without it asking you to format .
It`s likely that the drive from the laptop has a letter assignment of C: or D:
And that the dell system also contains two drives already listed as C: or D:
This is why when you connected the laptop drive to the dell system you were asked to format it.
Because a drive letter cannot be duplicated in the same system.
Windows by asking you to format the drive is trying to resolve the conflict.
By asking you to format the drive.
But you just need to force the laptop drive to another drive letter assignment to avoid the formatting.