Close all running 3rd party program such as Hotkeys, Cheat Engines, Key Pressers, Game Renamer ... etc.
Disable your antivirus
Disable Firewall
Check your Internet Connection
Right Click the Tantra Icon, Go to Properties and check "Run As Administrator" then ok.. (For Windows XP)
Right Click the Tantra icon, Click run as administrator (for Windows Vista or newer)
Check any virus attached on your computer
Check your Computer Specification, Check if you are able to reach the Minimum Requirement of Tantra
If you are playing other games.. Check if that games are using GameGuard, X-trap, and so on..
if this doesn't work....
Try to create a new account for windows .. Start->Control Panel->User Accounts->then create new user account then try to run tantra in your new user account (Windows)
And the best way to do (Only if you played tantra before)
Use System Restore.. Start->Accessories->System Tools->System Restore.. Try to remember when did you played your tantra and works well.. Click the date and perform a system restore..