I've looked around and found a simple way to reset things on your computer if you are running a Windows XP since it tends to happen to multiple system I have and I finally got fed up!
Here are a few steps that worked for me and I hope it works for you.

Symptoms: iTunes Store page is blank, Backups take long or not backup at all and most give errors like... Backup could not backup to this computer and so on... Well after a few webpages and allot of searching I found two steps that will help you out on this problem as it helped me on two laptops.

Just make sure you have everything closed and not have iTunes open. It may ask you to restart so try it and like always this help me out and I hope it does help you out. Please be safe.

Step 1: Go to the Start button and then go to run.

Step 2: Type in "cmd" without the qoutations.

*NOTE: If you are running Windows Vista, 7 or 8 you will need to run CMD as administrator

Step 3: Type this "ipconfig /flushdns" without the qoutations. Then press enter.

*NOTE: If you are running Windows Vista, 7 or 8 you will need to run CMD as administrator

Step 4: Type this "netsh winsock reset".  Then press enter.

*NOTE: If you are running Windows Vista, 7 or 8 you will need to run CMD as administrator

It will ask you to restart your computer so do that and after everything is up and running open iTunes and go to iTunes Store and see if displays the latest downloads. Also try to backup your iPhone and see if it does a full backup before syncing.

Let me know if this works for you and I really hope it help you since it was a beast when I lost everything on my phone don't want it to happen to yours.

Thanks,

-LeiNaD-