How to create usb bootable install media for Windows 8.1 in 2025

Really need more info here. Do you just want to revive the original computer? Is the drive bad or just a boot problem?  Sometimes if you can get the drive to startup it is possible ot clone it to a new drive as a replacement.  It would save some work if the clone works.  Otherwise you may need the original install disk and the drivers.  Some systems that had Windows 8 really needed those drivers to function. Even if you decided to upgrade to Windows 10 the drivers would be important.

One other idea:  It is possible that due to the age of your system the CMOS battery is bad.  I had two systems that 'forgot' the date (which can cause boot issues).  Mine were those #2132 coin type batteries.  Make sure the system is off and unplugged before changing though...