Thank you for help. Problem was related to insertion of SSD. After a number of times of refitting the SSD I was able to get computer to see the SSD. So now all good, computer much faster in speed.
I tried to install XPG SX8200 Pro M.2 2280 PCLE Gen 3x4 256GB SSD into Inspiron Desktop 3891 however computer does not detect it. The computer is fitted with HDD with Win 11. Wanting to change from HDD to SSD to increase computer speed. - SSD installed when SSD blank. Not detected by Disk Management or Macrium Reflect. - Then plugged SSD into USB port using an adaptor. Was able to clone full HDD files (C: plus other) to SSD using Macrium Reflect so SSD working fine. - Now refitted SSD that had been cloned from HDD into computer but still not detected. Also never seen the red LED in SSD ever flash. Do I need to make a BIOS change or some other change to get SSD detected Or does XPG SX8200 Pro M.2 2280 PCLE Gen 3x4 256GB SSD not work with this computer (I selected this SSD as working fine in another Dell G3 I7 laptop computer)
Inspiron Desktop 3891 does not detect XPG SX8200 Pro M.2 2280 PCLE Gen 3x4 
256GB SSD