High CPU usage when idle, many checks performed but still no clues

I've seen a lot of threads on this subject but thus far none have proved to be of any use to me.
Basically 2 days ago my computer started acting very slowly, and in looking at the performance tab in Task manager it's showing that with no programs open my CPU is running between 49%-79% all the time. I've looked up several threads on this suggesting to update drivers, which I did, to no avail. I completely wiped my hard drive and did a clean installation of windows and still the same, i tried installing on a brand new hard drive, still no difference, i have tried so many different procedures, i've taken out hardware, re introduced hardware, i booted up in safe mode and still high CPU usage, i've done clean boot, i can't honestly think of anything else to possibly try. I tried using KrView to see if there was any specific Kernels using up my processing power but apparently KrView doesn't work on a 64 bit system and when i found a version that was meant to work, it didn't actually display any information at all. can anyone please make a suggestion about what i can do? It's driving me crazy, as it is, it's taken me nearly 15 minutes to type this out because my machine is running so slowly.

Did you update Windows when after clean installing?

Have you looked at Resource Monitor / CPU tab to see if it shows what is using a lot of CPU ?
Sort the columns by CPU or Average CPU, descending.

I did, it says that the NT Kernel & system is taking up the highest CPU usage, i updated it as much as i could. It's just playing silly sods with me. We had a lightening storm the other day which resulted in a power cut and despite having surge protection it blew out one of my USB ports. Is it possible that it could have damaged my motherboard and that might be causing it?

If it blew out a USB port on the motherboard, it did damage the MB.
I don't know if that damage could cause your issue

I don't know how to test a motherboard for something like this.
Maybe call a local repair shop and see if they can do any testing ???

Perhaps others here will have better ideas ...

Problem solved. I ran a diagnostic and it showed my processor running an average of 156,000+ interrupts a second so i figure it must have been hardware related, even though i had removed all hardware and reintroduced it again slowly, i took my whole machine apart, air blasted it to rid it of any dust, put it back together and now it's running perfectly again, not quite sure what was different from me taking the hardware out this time from the first time, but it seems to have resolved it.

That's good news !
Thanks for posting back with how you fixed it, it could help someone else searching for the same issue