I have tried to install the software on Windows 7 Ultimate x64 in both English and Spanish and that appears to install correctly so it's possible that this is a Windows issue.
Are you installing from a CD or did you download the software from our website?
Try downloading the software from our website and installing it again. The software is available from http://www.picotech.com/software.html
Select the device in Step 1, then in the Step 2 drop-down menu, select 'PicoScope R6.5.78 (SR) for Windows XP (SP2)/Vista/7'.
If this does not work, you may need to repair your Windows installation. Backup any data and insert the Windows installation disc in the drive and starting the PC (you may need to select the option to boot from the optical drive from your BIOS window). When Windows Setup loads, select the option to repair the installation. You do not need to put a fresh install on the hard disk.