You machine probably has the trial issue of PRO on it. The trial is for 30 days, or 120 minutes, whichever occurs first. When the trial runs out, the machines will automatically revert to the FREE version.
There are no limitations to the FREE version as far as how you can use it. You can use it indefinitely, and for as many computers as you want. I have about a dozen, some people say they have hundreds !
The difference between the FREE and PRO versions are several features. You can print locally with PRO, you have a file transfer system to send files from one machine to another, the PRO version is having sound capabilities added. There may be one or two more differences. If you don't need the special options, the FREE version will be fine to use.
For a product comparison, check out the following link:
(DISCLAIMER: I am NOT an employee of LMI, nor do I have any financial concern in LMI. I am strictly a HAPPY USER of LMI products. I am using PC version and XP SP2. Other systems or versions may act different than described above.)