This issue mostly comes when we upgrade PSC ( appliances) , not able to open PSC in GUI mode.
This is certificate issue . there are 2 solution
1. Take snap shot and regenerate certificate then restart web-client service
2. Decommission affected PSC ( first check which PSC is pointing if you have 2 PSC) do not touch pointing PSC
3. Once Decomm delete it from disk and remove it from AD/DNS
4. Recreate DNS record
5. Deploy new PSC and join in Domain
6. Try IP/psc you should able to open it in GUI.