Windows 8 jumping between Metro UI and desktop during start up.

Step 1: Place the computer in Safe mode with networking

With the Windows Startup Settings screen (formerly advanced boot options) you can start Windows in different advanced troubleshooting modes so you can find and fix problems on your PC. In previous versions of Windows, you could get to this screen by pressing F8 before Windows started up. Windows 8PCs start up quickly so there's not enough time to press F8.

Follow the steps in the link below.

http://windows.microsoft.com/en-IN/windows-8/windows-startup-settings-including-safe-mode

If the computer works properly please perform the following step.

Step 2: Place the computer in clean boot and check for the issue.

Place the computer in a clean boot state and then check if it helps. You can start Windows by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate software conflicts.

http://support.microsoft.com/kb/929135

Note: Please go through the section: How to reset the computer to start as usual after troubleshooting with clean boot of the Kb article to boot the computer in normal startup after fixing the issue

Method 2:

Step 1: Follow the steps given in the Method 1 Step 1 to boot the computer in Safe mode with networking and then follow the given steps below.

I would also suggest you to scan your computer with Microsoft Safety Scanner, which would help us to get rid of viruses, spyware, and other malicious software.

The Microsoft Safety Scanner is a free downloadable security tool that provides on-demand scanning and helps remove viruses, spyware, and other malicious software. It works with your existing antivirus software.

 http://www.microsoft.com/security/scanner/en-us/default.aspx

Note: The Microsoft Safety Scanner expires 10 days after being downloaded. To rerun a scan with the latest anti-malware definitions, download and run the Microsoft Safety Scanner again.

Important: While scanning the hard drive if any bad sectors are found, the scanner tries to repair that sector, any data available on that might be lost.

The steps given here are valid only if your computer is not on Domain or Workgroup.

a)       Press Windows W + X Key. Click on Control Panel.

b)      Under the View tab unchecked Hide protected operating system files and Hide extensions for known file types.

c)       Go to the location

          C:\Users\(Your-old-Profile-Name)\.

          C: can be different according to the drive, where you have installed Windows 8.

d)    Copy all files except three files :

        NtUser.dat
        NtUser.ini
        NtUser.log

        If you cannot find the last file then there will be two log file with .LOG1 and .LOG2 extensions.

e)    Go to C:\Users\(New-User-Profile-name)\

f)     Paste all those copied files here.

g)    Now delete the old profile. You have successfully transferred all information and settings of the corrupted profile to the newly created User Profile.