Hi Vicky,
This issue is usually caused due to any third party hardware/software or due to any compatibility issues. I would like to know some information about this issue so that we could assist you further.
- Have you connected any external devices other than mouse and keyboard?
- have you installed any third party security software on your computer?
As a first step, I would suggest you to run the Upgrade Assistant to check if there are any incompatible hardware or drivers on your computer.
http://windows.microsoft.com/en-us/windows-8/upgrade-assistant-download-online-faq
If there are no incompatible hardware or software on your computer, then I would suggest you to try the following methods and check if it works for you.
Method 1:
If you have connected any external devices other than mouse and keyboard, then try disconnecting it and then try to upgrade to Windows 8.1.
Method 2:
Reset Windows Store Cache and then try upgrade to Windows 8.1 and check if it helps. This will help you reset the missing or corrupted Windows Store Cache.
Follow the steps to reset Windows Store Cache:
- Swipe in from the right edge of the screen, and then tap Search.
(If you're using a mouse, point to the lower-right corner of the screen, move the mouse pointer up, and then click Search.) 2. Enter run in the search box, and then tap or click Run. 3. Enter wsreset.exe in the Run command and then tap or click OK.
Method 3:
Place the computer in Clean Boot state and check if the issue persists. This is to check if the issue is caused due to any third party program/app.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7 or in Windows 8/8.1:
http://support.microsoft.com/kb/929135
Note: After clean boot troubleshooting step, refer to the section "How to reset the computer to start as usual after troubleshooting with clean boot" in the provided link to return your computer to Normal startup mode.
For further reference, you may refer to the following Microsoft Help article.
http://windows.microsoft.com/en-us/windows-8/update-from-windows-8-tutorial
Please reply with the status of the issue so that we can help you better.