You will need to yank the heatsink, clean it off and read the info on the chip I guess.

If it won't even power on, its probably only good for scavenging parts. But it could be just the power supply. Did you get it from a dumpster?

If you know the dell service number, you can enter it on their web page and see what it was originally delivered with.

All good points. You did not mention if the system will power on. Assuming it does try the following.

It is pretty easy to tell what CPU you have in the system once it is powered on. Click on the search icon next to the Start icon. Then type in sysinfo. Click on the system information app and you can see a number of specs about your system including CPU type.

Normally there is a label on the case saying "core i3 inside" or "core i5 inside" or "core i7 inside". Otherwise you can use the serice tag to check the original system configuration on the Dell website.

i'm shocked you can't turn it on. The PSU dead? (never seen a post like this in 10 years, ID fix that first)

only the chip top answers that, there is no other way. (your serial number on your service tags tells dell what they shipped new, but lost of refurbs sold are already upgraded. making that number useless)

8 year old PC things change in 8 years time, magical upgrades happen, and often now, gamers love to buy them. hint hint pre upgraded.

remove heat sink and grease and read to of INTEL CPU chip..

if the PSU works boot to linux demo disk and use utilities there to scan the CPU,. (easy)

or boot to windows PE disk and do a system information command. gui pops 5 lines down is CPU real name.

Thanks guys !!  That is what I suspected is that everting inside "looks" the same without tearing it down to the CPU.