Digital multimeter, voltage meter... you said external hard drive, you have to have some way of powering the drive, usually a usually a step down transformer, i.e., a wall wart/ power brick!
Sorry Marcellis22 ,,This external hard drive is only connected to the computer by USB cable .No powerfeed involved Plugged it this morning in a different spot on the tower itself instead of to my 7 spot hub . It showed for half a minute and then I got the message : "Windows delayed write failed"
If you're using a drive that's powered by the USB cable you should plug it directly into one of the USB ports on the computer case itself. A hub has to distribute power from it's one connection to the computer down to multiple devices and it probably doesn't have enough to run the drive.
The prblem has been solved . Thank you all for the help !!