You may have too many applications running in the background,
like more than one Anti-Virus software application both set to run
in the 'Active Scanning' which will slow things down.
If you want to dig deeper:
Try Autoruns from the MS Windows SysInternals site:
http://technet.microsoft.com/en-us/sysinternals/bb963902.aspx
AutoRuns will show/list all apps/etc. that load/run when you first boot ...
(the 'Boot Execute' tab),
when you logon (the 'Logon' tab) and other programs that load
(grouped by labeled tabs) for easy viewing.
It also provides the ability to selectively allows you to stop
(use with care) any program that you don't want to load.
You can undo any changes you have made.
Note: To get additional details on an item in the list you can't
readily identify you may need to highlight the item (right click) and use
the 'Search Online' option to get the details,
especially useful for the more obscure items in the list.