after several failed attempts to install F-secure Safe,all my lisences are gone and my computer is still unprotected
You need to run the F-Secure Uninstallation Tool, which will clean up the failed installation attempts, then you can start again. If you have "run out" of licenses, as Ukko said, you can go into your SAFE Portal and remove any unused devices from your account, which should free up the licenses again, or, when you go to reinstall the product, if there are no spare licenses, it should prompt you to re-use an existing, inactive license, so either way, you should not have lost your licenses through the failed installations.
The above is assuming that you are using a compatible version of Windows (Vista SP2 or newer), and that you have no conflicting software on your machine, such as another anti-virus product. If you had another AV product, and have just uninstalled it, then I would recommend that you find and run the relevent product's uninstallation tool, to remove any remnants of it, before attempting to install F-Secure again. Let us know if you need help with that.
Sorry for my reply.
What was the trouble with installation (any installers notification prompts about mistake?! or something else?). Also with F-Secure SAFE -> there should be available option like 'login to your account' (under My F-Secure) and manage 'installed devices' (like release license/remove device);
Or with next installation-try there will be prompt about re-use licenses (from unused devices).
So, if you have troubles with installation-process -> you can try direct Support Channels:
Or just give more information about your stuck with installation.