I think your hardware is unsupported. Did you check the VMware HCL?
What is the processor model.
Most likely your hardware is not supported.
Enter your model here
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As others have already mentioned here, a Dell Optiplex 755 is not a suitable hardware platform for ESXi. However, it is possible to install ESXi on these machines, but you probably need a different CPU.
The error message looks like a CPU is installed that is no longer supported or accepted by ESXi 6.5. See the release notes for a list of unsupported CPUs for ESXi 6.5:
And you may find more information in the Dell communities:
Check this , it may helpfulRAJESH RADHAKRISHNAN
VCA -DCV/WM/Cloud,VCP 5 - DCV/DT/CLOUD, ,VCP6-DCV, EMCISA,EMCSA,MCTS,MCPS,BCFA
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