So VoiceAttack is showing it cannot detect an input device when it starts, currently? What is the exact message (left click the log entry to select it, then right-click the log entry and choose "Copy" and paste here)?
Does the "Windows Speech Recording Device" dropdown on the "Recognition" tab of the VoiceAttack options window show any devices?
Is the Windows Speech Recognition application working?
Something else to check is the "Allow desktop apps to access your microphone" option, found in the Settings app under "Privacy", in the "Microphone" subsection.
Note that the "Allow desktop apps to access your microphone" option, specifically, is relevant to VoiceAttack, however the "Allow apps to access your microphone" option must also be enabled (the former cannot be enabled without the latter).
Normally this option is enabled by default, and a Windows notification should pop up when you start VoiceAttack if it's disabled, but it's worth checking just in case.
Also, have you tried running VoiceAttack as administrator (click the wrench icon on VoiceAttack's main window, enable the "Run VoiceAttack as an Administrator" option on the "System / Advanced" tab of the VoiceAttack options window, click "OK", then restart VoiceAttack to run it as administrator)?