Are you coming from Virgin Media Security, or another security product? If so, you need to make sure the previously installed product is completely removed from the machine before starting the F-Secure installation. You can find more info on uninstalling VMS here:
Or if you have / had another security product installed, you'll find a list of Uninstallation Tools by clicking the link.
In that case, I would suggest running the VMS Uninstaller again, just to check nothing was left behind, then, if necessary, run the F-Secure Uninstallation Tool, then start the F-Secure installation again.
If none of the above works, then you'll need to submit a support ticket to F-Secure, with an attached FSDIAG, which should give them some help in diagnosing the installation issue. You can download and run the Support Tool from here:
That will create a zip file on your Desktop, which you can then attach to the support ticket, from here:
Good luck, and let us know how things go.