This is likely either to be bad "Add-ons" or malware.
I would first try IE's "No Add-ons" option. Go to Start > All programs > Accessories > System Tools > "Internet Explorer (No Add-ons)" option.
Use that to see how IE performs and if it works much better, then you know that you have a rogue add-on. Then close that IE down, open your usual IE, then go to Tools > Manage Add-ons and start testing. It will probably mean an elimination test, disable an add-on, test, if no change move on to the next add-on.
If that fails then you move on to virus and malware checking. Update your anti-virus software then run a full scan. Then download and install the free versions of Malwarebytes Anti-malware and SUPERAntiSpyware
When installed, run each one, one after the other, (not both together), update them, then run full scans.
Hope that helps.
My IE7 has begun to slow down considerably. Now, it takes up to 20 seconds after opening a webpage to get anything to happen. Can't even scroll down. What happened?