Hello there, DanielDias.
Do you have a Snow Leopard (OS X 10.6) install disk? You would have had to have that version of the operating system installed on the Mac to have had the App Store to have purchased the Lion download. For reference, see requirements:
With that exact OS installed, you should be able to download and install Lion from the App Store by following these instructions:
Thanks for reaching out to Apple Support Communities.
As pointd out by Pedro the only way to buy lion was to have snow leopard 10.6.6 or above installed on your mac. To have snow leopard of any point release installed on your mac you must of had and hopefully still have a retail snow leopard upgrade dvd.
You must find that dvd and upgrade to snow leopard or buy another one from apple. Once you have snow leopard 10.6.3 installed on your mac from the upgrade dvd you then update that to 10.6.8. Once that is done then you can use the mac app store, log in using the same apple id you used when you bought lion and it will be in your purchases area of the mac app store.