Hi ACA'ers. Just wanted to share tip hopefully to save someone else the pain.
I'm still using 2013 and often it gets stuck on the start up screen. I now know this is because certain peripheral routines are stuck for some reason but here's something to try that works for me.
I'm on Windows7 64bit so you might have slightly different path.
Open ACA and if it gets stuck on the opening screen, see what loading message is displayed and try this.
Open your Windows Task Manager (by pressing Control-Al-Delete keys at the same time and selecting the WTM option if it gives you a menu.).
Click the first column tab at the top to get them to sort alphabetically.
You will see several items starting with Ac... like AcSettings, Ac..Cloud, maybe AcBrowserHost and also AdSync
If you look at the start up screen you can usually see that it's stuck trying to load the adesk cloud routine etc so in the WTM right click on these routines and choose 'end process'.
They will restart usually but this time will not stop ACA from starting up. For me there is no issues doing this but if for e.g. you use the cloud there may be issues, I suggest post a comment here for others.
nrename the AcDgnLsTrans.dbx to AcDgnLsTrans.dbx.bak found at C:\Program Files\Autodesk\AutoCAD 2013\
Do not delete the file