The hardware conditions of a drive can be checked by viewing its S.M.A.R.T. data. To see it, right-click the drive and select S.M.A.R.T. on the shortcut menu.

Disks panel with the S.M.A.R.T. data of a healthy disk

When R‑Undelete determines hardware problems with a hard drive, it shows the exclamation mark on the drive icon. Check the S.M.A.R.T. data and decide what to do with the hard drive.

The yellow exclamation mark signals hardware problems:

Disks panel with the S.M.A.R.T. data of a disk with small hardware problems

This sign indicates that some small problems with the disk are possible in the future, caution is required when working with the hard drive, and these parameters should be checked regularly.

Disk imaging   is recommended. Then files may be recovered later from that image.

The red exclamation mark signals that the hard drive is in critical condition:

Disks panel with the S.M.A.R.T. data of a disk with heavy hardware problems

This sign indicates that the hard drive conditions are critical and chances of hardware failure are high. The best recommendation for this case is to stop working with the hard drive and bring it to professional data recovery specialists. Work with the disk is possible, but at your own risk. Disk imaging is very strongly recommended. Then files may be recovered later from that image.