Pegatron M2N78-LA Violet3-GL8E CPU-support

Hello!  I am trying to replace the CPU in my old HP P6140sc. Current cpu is AMD Phenom II X3-720 (HDX720WFK3DGI), bios v.5.08.
When installing Phenom II X4-955, it says "Unsupported CPU installed." I can get to Windows 10 if I press quickly F2 when the error notification appears but I can't get into bios!

Specsheet of motherboard says that Phenom II X4-955 should be supported:

Socket type: AM3
TDP: 95 watt
Motherboard supports the following processor upgrades

AMD Phenom II X4 9xx/9xxe/8xx Quad-Core (Deneb)
AMD Phenom II X3 7xx/7xxe Triple-Core (Heka)
AMD Phenom II X2 5xx (Callisto)
AMD Athlon X4 6xx/6xxe (Propus)
AMD Athlon X3 4xx/4xxe (Rana)
AMD Athlon X2 2xx/2xxe (Regor)

Do I need some kind of modded bios to get the bios and cpu work? Can you help me with this?

Computer:
https://support.hp.com/us-en/product/HP-...el/3999096

Motherboard:
https://support.hp.com/sg-en/product/hp-.../c01742903

Latest available bios (5.08) from HP-website:
https://ftp.hp.com/pub/softlib/software1...p46427.exe

CPU that needs support:
AMD CPU Phenom II X4-955 HDX955WFK4DGM 3.2GHz Socket AM3 TDP 95Watt
http://www.cpu-world.com/CPUs/K10/AMD-Ph...K4DGM.html

Thanks!

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