I have seen issues with the Policy.Invoker running high on resources at startup - there is a batch file that I found on here to clean up the XML files & clear up this issue - I have only seen this on 1 pc so far - we have around 2000 in our environment.
Here is the Policy.Invoker batch file threadCleanup for "policy.client.invoker.exe" (batch file)
Other causes that are more common that I have seen are the Computer Browser Service & HP Health Check - I have a patch set up to disable those. I have also seen antivirus updates cause this slow start issue. I have waited 20-30 minutes for the welcome screen to finish spinning on a couple of pc's with recent Symantec A/V updates.