Question Newly reformatted laptop suddenly getting slow internet via WiFi ?

I just reformatted my old laptop, after a successful installation of OS I can't use the internet properly, It only shows 1 bar of wifi even its already beside of router and getting RCed and DCed (it used to work properly before I reformatted it, getting decent speed and full bar of wifi). I tried to connect on another wifi, the result is the same 1 bar and getting RCed and DCed.
My 2 internet works perfectly on my pc and other gadgets.

i3 4005U | 4gb

Things I tried:

  • -Restart router
  • -Restart laptop
  • -Device manager: disable then enable network adapter ; reinstall network adapter
  • -CMD: netsh int ip reset

Note: I haven't tried cables as my laptop LAN port is not working, and I am not really going to use it with cable internet. I require wifi.