Dell Optiplex 9020 Micro not powering up after upgrading SSD to Crucial 1T SSD.

Powered up first time after upgrade, and ran for a couple of hours without any problems.

Next day it would not power up!

Have gone back to the original 128GB drive, but same problem.

Power light comes on and about 30 seconds later a message appears on the monitor,

2 seconds later the PC powers down.

No chance to enter BIOS setup etc.

Hoping somebody has a solution!

Thank you...