Help! Several issues after disassembling & reassembling!

Hello, I'm very unexperienced with this type of stuff, so please bear with me

My Thinkpad, that I recently took apart in order to clean out dust and replace thermal paste, won't work properly!

I watched a tutorial on YouTube (if needed I can link), but I lost a screw and I believe I misplaced some of them (that is my own mistake)

• It won't start up unless I plug it up while it's booting, and even then there are still issues; the fans spin for a second but then it turns off, and I worry it may be something that is unrepairable!
• Once I do get it started up, if I close it, it won't show anything on the screen and it'll beep 4 times
• Sometimes the power button will just blink 3 times and it won't boot
• It only works properly if I don't unplug it or close it

There are also issues with it that existed before I ever took it apart, such as:

• The new (off-brand) battery doesn't work properly, it'll shut off seconds after turning it on even if it is fully charged
• The WiFi sometimes refuses to work (does not show up at all) after I leave it closed/sleeping for a long period of time, and when I try troubleshooting, it tells me to enable 'wireless capability', this usually fixes after a restart

When I took it apart, I took things out such as the RAM, SSD and took out a lot of screws, and unplugged a few things. I'm afraid I may have messed something up, or forgotten to plug something back in.

I believe I put a lot of screws in the wrong places, and may have put some longer screws where shorter screws should have went.

I put everything back (to my knowledge)

Something I will note: I lost the screw to the disk drive, so I used a (longer) screw to replace that one. I'm thinking that may have something to do with it.

Please, I just recently got this laptop for Christmas and I really like it, I don't want it to be broken.

Thanks!

Update: Tried to power on with battery (not a charger), and it powered on just fine, but the problem with it beeping 4 times (4 times in a row) after closing it still persists

I also found the correct screw and replaced the longer screw with the proper one, however that didn't make a difference