Did you uninstall it from the proper location? What is your OS and what have you done so far to get rid of it? Here's where you can look for what's causing the popup, however. Go to Start/Programs/Startup. If you see anything there related to the program, right click and delete it. Next, go to Start/Run and type "msconfig" (without quotes). Go to the Startup tab and look for anything that sounds like PC Booster and uncheck it. You will need to restart the PC to make this change take affect. Good luck.
I downloaded trial version of PC Booster. 14 days trial period has expired but I can't seem to get rid of the reminder box reminding me of the expiry everytime the PC is switched on! Please help.