Standard Tech2Win installations from GM's TIS2Web usually require a paid subscription and expire after 30 days. The common "crack" method to keep the software working involves these steps:

Once those 30 days are up, the "lock" icon on the status bar closes, and you must reconnect to the GM server to renew the lease. 2. Making it "Work" (The Patch/Crack Approach)

[How To Install] VXDIAG - The poor man's Tech2 | DF Kit Car Forum

While a "cracked" version may offer full diagnostic access, there are significant hurdles: Module Flashing