if this is your mobo: https://support.hp.com/in-en/document/c02185182
then:
Motherboard supports the following processor upgrades:
Core 2 Duo E8xxx series (W)
Core 2 Duo E7xxx series (W)
Intel Pentium (W) E5xxx series with Dual Core Technology
Celeron Dual Core (C) E1xx0 series
which means probably it's a LGA 775 motherboard, so no i-series cpu (i3,i5,i7) support for that mobo
Seeing that this is the motherboard you're referring to: https://support.hp.com/in-en/document/c02185182
You're not allowed to go to the Core i3 range of processor. Rather you're limited to sticking with LGA775 processor parts, effectively the Core 2 Duo's.
Motherboard supports the following processor upgrades:
Core 2 Duo E8xxx series (W)
Core 2 Duo E7xxx series (W)
Intel Pentium (W) E5xxx series with Dual Core Technology
Celeron Dual Core (C) E1xx0 series