Security software is the most likely cause of peculiar behavior after TaxAct updates or installations, because it can interpret modification of the program's main EXE file as malicious behavior. Malicious software, or malware, will often change and hijack legitimate programs. Security software may quarantine the program, prevent it from running, block access to other files on the computer, and block outbound transmissions.
If your TaxAct program has stopped working after an update, you should consult information for your security software regarding how to allow the TaxAct program to perform updates and installs. You may need to check for exclusion or whitelisting settings to trust the TaxAct software to run. In some cases you may need to check the quarantine contents to see if the TaxAct installation file or executable were picked up.
In the meantime or otherwise, you could disable the security software when updating or downloading and installing TaxAct. Most security software has a temporary disable setting. If you disable the security software but the problem with TaxAct persists, you may need to download and install the TaxAct federal or state program again while the security software is disabled.