Identifying issues with cores and threads
You need a CPU with at least 10 cores and 20 threads. Your PC should display this configuration, but if it doesn’t, adjust the BIOS settings to match.
You purchased it secondhand, and I suspect you were taken advantage of.
The cache appears correct; attempt to reset CMOS and check if the cores resume functioning.
I purchased it in its original condition.
Your system is using an older Windows version prior to the 10900K upgrade.
Did you verify that option in msconfig, or is it already set?
Open msconfig, remove the processors box, restart and allow Windows to allocate remaining CPU cores. Think about a complete Windows update.