It could be a port conflict or mismatch.
Or if Sql were set to use dynamic ports and there's another sql instance running...
Sql by default wants port 1433, but this can be changed.
See KB51703 in the McAfee Knowledge base and also walk through all the options listed in KB51670 - 'Unable to log on to the ePO 4.x console (Troubleshooting - Master Article)'
Knowledge base link canbe found here: