how to find the serial number of my pc without opening it

Easier if you don't want to touch PowerShell: restart and go into the BIOS setup (F2, F10 or Del depending on make). The main screen usually lists the serial number. On a laptop it's also on the sticker underneath, often next to S/N, sometimes inside the battery compartment on older ones.

Open PowerShell and run: Get-CimInstance Win32_BIOS | Select-Object SerialNumber The old wmic bios get serialnumber command still works on a lot of machines, but Microsoft is phasing wmic out so don't be surprised if it's missing. Works for any Dell, HP, Lenovo etc. If you built the PC yourself it'll probably come back as "To be filled by O.E.M." or blank, because nobody wrote a serial into the board. In that case the only serials that exist are the ones on the individual parts.