When I go to insert a DWG file in Inventor 2014 I get nothing for the preview. I just click ok and move forward. It brings it in but it is also very slow.
Which OS are you using?
There's a known issue with Windows 8.1, see below link.
When importing or inserting, are you using Apply E
Some other things you may want to try:
Another post, below recommends the following solution for Windows 8.1, but the same solution may apply for Windows 7.
(First lower UAC and temporarily disable anti-virus software)
1) Press [Windows] key to open the Windows' start page
2) Type "cmd" to find "Command Prompt" > right mouse click on it
> select "Run as administrator"
3) On "Administrator: Command Prompt" window, type
cd "c:\program files\autodesk\Inventor 2014\bin"
4) Wait for 1 min (inventor will be executed background then exit silently)
I hope this is helpful. Please keep us updated on your progress.
Is the problem file specific or with all dwg/dxf files?
Have you installed any Beta software, recent updates, etc..?
One other solution you may try is to uninstall/resinstall DWG TrueView 2014.
I hope this helps. Please let me know if there is an update.