On April 8, 2014, Microsoft will end support for the decade-old Windows XP and Office 2003. This means you will no longer receive updates, including security updates, for Windows XP from Microsoft.
Without critical Windows XP security updates, your PC may become vulnerable to harmful viruses, spyware, and other malicious software which can steal or damage your business data and information. Anti-virus software will also not be able to fully protect you once Windows XP itself is unsupported.
Software and 3rd Party Issues:
Many software and hardware vendors will no longer support their products that are running on Windows XP as they are unable to get the Windows XP and Office 2003 updates. For example, the new Office leverages the modern Windows and will not run on Windows XP.
More details can be found here –> http://www.microsoft.com/en-us/windows/business/retiring-xp.aspx and http://www.microsoft.com/en-us/windows/endofsupport.aspx