I too had the blank iTunes Store window after downloading iTunes 10.4. This appears to be a widespread problem for 32 bit and 64 bit Windows 7 systems. There are several "simple" fixes that I found online that did not work for me and I absolutely refuse to pay Apple Support $50 for their help. The following solution worked for my 32 bit and 64 bit Windows 7 laptops. My solution was to downgrade the iTunes software. I uninstalled iTunes 10.4 and reinstalled iTunes 10.3. I did not backup my songs and I did not lose any songs. I learned that when you uninstall iTunes the database is backed up automatically and put in the "Previous iTunes Libraries" folder. But if you are worried and want to be ultra safe go ahead and back it up yourself. Here are the steps to properly uninstall iTunes 10.4 and reinstall iTunes 10.3:
1. Go to Control Panel>Programs>Uninstall
2. Uninstall the following Apple programs in the following order:
c. Apple Software Update
d. Apple Mobile Devices Support
f. Apple Appllcation Support
3. Reboot PC
4. Find, Download and Install iTunes 10.3 (you can find it at FileHippo.com)
If you start iTunes now you will get an error message saying that the current iTunes library was created by a newer version of iTunes. To correct this:
5. Go to your Music>iTunes folder and delete the "iTunes Library.itl" database file
6. Within this iTunes folder find and open the "Previous iTunes Libraries" folder and locate the most recently dated "iTunes Library (date).itl" database file.
7. Copy and Paste this file back into the iTunes folder
8. Rename this "iTunes Library (date).itl" file by removing the date. It should say "iTunes Library.itl"
9. Reboot PC
You are finished. Good Luck and I hope this helps.