3 long beeps 5 short beeps

[harryt]

My HP desk top PC will not start up. My power switch flashes red with 3 long beeps followed by flashing white with 5 short beeps. 

I replaced an i3-6100 with an i5-9400. The socket number on the board is LGA 1151. The i3 works fine. I want to upgrade with the i5. The i5-9400 is for socket LGA 1151. If I put the i3 back in it starts up and works fine. Any help is much appreciated

[AlHill]

It is VERY likely that your system does not support the i5-9400.  Being socket compatible is not enough.  You must also be BIOS compatible and chipset compatible.  Contact HP and ask them if the i5-9400 is compatible with their bios.   Also, stop using the i5-9400 lest you damage it or the motherboard, or both.

Doc (not an Intel employee or contractor)
[Windows 11 is the new Vista]