When you removed the size 2032 CMOS battery, did you replace the battery(s) with new one(s)?  I've seen boot loop problems before in this forum due to bad batteries.  That would be the first place to start 
Excuse me Please: I am experiencing a very convoluted issue with 3ea. o790s SFF and need assistance in 1. understanding what happened, and 2. finding a means to restore functionality. The below peripherals installed into the first 790, it need be stressed, have been performing flawlessly on nearly a daily basis, and for many hours within a day, for at least the last month and a half since being upgraded. upon discovering the problem, the Kubuntu2204, running an off-line Steam, and two instances of an MMORPG on character select screen was frozen, hard. Also, the illuminated mouse and KB were also DARK (but the mouse laser was working/powered-on) Each was setup identically,  (swapped out components into subsequent 790s) CPU: either i7(-2600) or i3 RAM: Crucial 4GB DDR3L-1600 GPU: Radeon RX 6400 Dell support page indicates that boot code 1, 2, 4; and 3, each refer to the CPU. which the newly installed i7 and the replaced i3 have both been reseated/replaced, with no change to the boot codes. HOWEVER! (and this is the weird part) while researching the codes/possible fixes, i just left the 790, without NIC, GPU, or SSD to boot loop, seemingly never getting to the boot logo; yet, it did seem to arrive on the "can not find hard drive" part of the boot process ONCE. So I left the bios screen up while i continued researching,... the 790 then seemed to reboot on its own, and return to boot looping. On a second and third SFF790, I initially booted them without any peripheral addition, no problem, bios identified CPU, the one stick of memory, and such. On unit #2, i reinstalled ALL of the previous system's peripherals in on go (BAD idea!) and the boot looping with same error codes occurred. The third unit, i took the process much slower, first installing the 16GB ram, which booted fine and sat on bios for a good period of time. (it need be stated, that when booting these 790s, without ANY peripheral change, that initially, they seem to display the same 1,2,4;3 code, then reboot, then boot normally on the second attempt o.O) I then installed both the TP-Link Gigabit Ethernet PCI Express Network Card (TG-3468) and the Radeon RX6400 (i know, now, that i should have only did ONE at a time) and upon powering up, the boot loop occurred. at least this third unit i know its bios firmware was A18, i do not know or recall the former two. I have no means to test either the GPU, or NIC. Can any of these damage a MB into thinking something is wrong with the CPU? is this a permanent break? the removing of the CMOS battery as well as temporarily using the pswrd jumper to short the RST jumpers has seemingly no effect. I am the limit of my expertise, and hope these symptoms might be familiar to those more experienced than i. Thank You for your time in assisting me in this. HCA   p.s. the system i am using to post is also 790, also 16gb ram, also rx6400 GPU, only difference is its NIC: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06)Subsystem: Realtek Semiconductor Co., Ltd. RTL8111/8168 PCI Express Gigabit Ethernet controller. PCIe if memory serves. Not sure if NIC difference is an important detail,...
o790 (x3) 1,2,4;3 DEAD for u/k Reason