After installing a new CPU chips, the computer will power on when plugged in, but no beeps, no monitor response, can only shut off by holding power button 10 secs. Works when put original CPU back in. Then can turn on with power button but still no beeps or monitor response.
Orig CPU: 600EB/256/133/1.65V (SL3XT)
New chips 1.2Ghz/256/133/1.47V &
1000Mhz/256/133/1.7V
All in PPGA Socket 370.

Followup clarification...

After installing a new CPU chips, the computer will power on when plugged in, but no beeps, no monitor response, can only shut off by holding power button 10 secs. Then can turn on with power button but still no beeps or monitor response.
Works when put original CPU back in.

No time for in depth research, but it sounds as though your motherboard doesn't support Tualatin core CPUs. I'm almost certain a 1.2 P3 would be a Tualatin. Do a search on the CPU code. You might check and see at HP if your board supports Tualatins. If it is a Coppermine, you may have a bad CPU. They do make S370 converters that would allow you to use a Tualatin, I recently bought one for $12.00 shipped on Ebay.

That or you need a Bios update. I remember when the Vencie cores for the Athlon 64 came out Some motherboards wouldn't post until they got that Bios update. A lot of Nforce 3 boards had that problem with those cores.

Repo man is correct the 1.2 p3 was a Tualatin core.

The board that you have sounds very much like a copermine, the 2 dont mix, and to the best of my knowledge a bios update does not work.

I had an old Asus CUSIM which could not run Tualatin core One needed the TUSIM, same board exactly same spec but the micro code could was different.

I think you might have the same problem..

I am not aware of converters but what repo man said sound like its worth a good look.

IF IT AINT BROKE, DONT FIX IT

A8N-SLI Deluxe
AMD X64 3500+ Wnchst
Corsair 2x512 DDR400 Dual Channel
GV-NX6600128D PCIX Graphics Card
Ggbyte GT Pro CPU Cooler
Zalman VF700-CU VGA Cool

Repoman and Janos are right. The Coppermine core P3 and Celeron with socket 370 FCPGA go only up to 1,1GHz. The Tualatin core with socket 370 FCPGA2 start at 1GHz and go up to 1,4GHz. I also read about a few Coppermine core build with FCPGA2!
I know for sure because I needed a Coppermine core FCPGA to upgrade my old Asus P2B slot1 board because the adaptercards only support FCPGA but no FCPGA2 which is also true for older FCPGA boards!

You may check out www.powerleap.com because they are very good with such adapters. They even offered a slot1 adaptercard that supports FCPGA2 Tualatin core cpus but I found that out too late!

One of these ought to allow you to run that CPU.