Windows System Will Not Go To Sleep

I am having a frustrating issue where my Windows computer will not go to sleep no matter what I try. When I click on the Sleep option from the Start menu, the screen might turn off for a second, but then the computer immediately wakes back up or just stays on with the fans still running and the power light still solid. I have already checked my power settings in Control Panel, made sure that no devices like my mouse or keyboard are allowed to wake the system, and even run the powercfg -lastwake command in the terminal, which showed something about a network adapter waking the PC. Has anyone else dealt with this problem, and what step-by-step solution finally fixed it for you? I would really appreciate any advice you can offer. Thank you.