1. If you're launching DSM on a workplace domain network, try switching to a direct internet connection temporarily and launch the software as an administrator.
2. If you can only use a single network at your workplace, try asking your IT admin to switch off FIPS mode locally for your PC's internet adapter (Wi-Fi or Ethernet) settings:
They can change this through Control Panel-> Network and Internet-> Network and Sharing centre -> Change adapter settings. Pick the internet adapter based on how you usually connect to your network- wired ethernet or Wi-Fi. Right-click on the adapter and click 'Status'. Then, open Wireless Properties -> Security-> Advanced settings. Toggle the check off for the FIPS option and click OK to save & exit.
There is more guidance on how IT admins can change this via local group policy here: https://www.howtogeek.com/245859/why-you-shouldnt-enable-fips-compliant-encryption-on-windows/
FIPS mode blocks access to newer cryptographic schemes that have not been FIPS validated. This does not mean the DesignSpark software activation mechanism is any less secure. FIPS stands for “Federal Information Processing Standards" that are published by NIST of the US federal government.
3. Download the latest version of .NET Framework (at 4.7.2, as of 6 August) and uninstall any previous versions from the 'Programs and Features' area.
Download here: https://www.microsoft.com/net/download/thank-you/net472
4. Windows update (KB3013455): Please uninstall the update through 'Add or remove programs' -> 'view installed updates'.
Once uninstalled, please restart the computer and try launching DesignSpark Mechanical again.
To avoid installing the update again until it's fixed, you can right click on it and select 'Hide Update'.