Hi,
Do you have any third party security software installed on the computer?
I suggest you to try the following steps if you are unable to install
Method 1:
Disconnect all the external devices (printers, scanner, USB (universal serial bus) drives, etc) except mouse and the keyboard and then try to install Windows 8.1
Method 2:
If the issue persists, I suggest you to disable the antivirus/firewall software and check if you are able to install.
Important Note: Antivirus software can help protect your computer against viruses and other security threats. In most cases, you shouldn't disable your antivirus software. If you have to temporarily disable it to install other software,
you should re-enable it as soon as you're done. If you're connected to the Internet or a network while your antivirus software is disabled, your computer is vulnerable to attacks.
Method 3:
You can also place the computer in a clean boot and then try to install the upgrade. Clean boot will eliminate the software conflicts.
You may follow the article mentioned to perform a clean boot.
Perform a Clean Boot
Follow the instructions (Step 1 for Windows 8) given in this link to perform a clean boot:
http://support.microsoft.com/kb/929135
Note: After performing the troubleshooting steps in clean boot, follow these steps to return the computer to Normal startup mode.
a) Press the ‘Windows + R’ key on the keyboard.
b) In the ‘Run’ windows type ’MSCONFIG’ and click ‘Ok’.
c) On the General tab, click the Normal Startup option, and then click ok.
d) When you are prompted to restart the computer, click Restart.
Hope this helps.
Please post back with the status of the issue and we will be glad to assist you further.