Question CPU causing beep error on startup

[idk12345121]

So I bought a dell optiplex 7020 minitower, and paired it with an i7-4790s. I tried booting up the PC and I got this beep pattern: 1-3-2. 1 beep, then 3 beeps, then 2 beeps. I looked it up online and everything just tells me it's a memory issue, but whether the memory is in the PC or not, the error still occurs. But whenever I take the CPU out or disconnect the cpu power connector, the error doesn't occur. Please for the love of god, it's been making me so mad, so can someone please help me?
(Yes, I have made sure all cables are plugged in.)

 

[COLGeek]

What CPU did it originally come with? Do you know whether this system worked before now? Also, do you know if the most recent BIOS version is installed on the motherboard?

https://www.dell.com/support/home/en-us/product-support/product/optiplex-7020-desktop/drivers

https://www.dell.com/support/home/e...scode=wt64a&productcode=optiplex-7020-desktop

 

[idk12345121]

What CPU did it originally come with? Do you know whether this system worked before now? Also, do you know if the most recent BIOS version is installed on the motherboard?

https://www.dell.com/support/home/en-us/product-support/product/optiplex-7020-desktop/drivers

https://www.dell.com/support/home/e...scode=wt64a&productcode=optiplex-7020-desktop

It never came with a CPU; it was a barebones.
When I bought it I'm pretty sure it said that it was tested before being sold.
I don't know if the most recent bios version is installed.

 

[COLGeek]

CPU socket pins all good? What make/model memory did you install? As I recall, those old Dells were very picky in terms of compatible memory.

Where did you purchase from?

 

[idk12345121]

CPU socket pins all good? What make/model memory did you install? As I recall, those old Dells were very picky in terms of compatible memory.

Where did you purchase from?

I purchased 16gb of ddr3 1300mhz ram that's supposed to be compatible for dell inspirons I think? And cpu pins are good. And I purchased from Ebay.