There was one instance similar to yours a while back where the .NET 2.0 was installed but had become corrupted causing Sentinel not to run after being installed. The following procedure was successful in getting his Sentinel to run.
To repair Windows .NET framework..... in the Windows search bar, search for "features", and then click on "turn Windows features on or off".
Once that window populates, look at the checkbox next to ".NET Framework 3.5 (Includes .NET 2.0 and 3.0)”.... it's usually the first line in the features window. Un-check that box, click "ok" and reboot the computer.
Now go back to the same area noted above and re-check the box for ".NET Framework 3.5 (Includes .NET 2.0 and 3.0)”. Click ok and reboot the computer again. Now see if Sentinel will run.
If that doesn't help, you'll need to start tracking down other suspects that may be blocking Sentinel such as anti-virus software, firewall settings etc.