Just try doing a system re-boot. There is a screen switch in the DirectX when using Showcase, possible after exiting Showcase it didn't fully switch back because of your integrated graphics card.
I made full reinstall of Windows and installed all new drivers but the problem is still there. It feels like the fps dropped from 100 to maybe 60 while rotating the parts. Looking from the task manager the processor usage doensn't go higher when I rotate the parts. I don't remember how high the memory usage was before, but now it's 3,3gb/4gb.
I don't have prolems with Showcase. It's not even installed now. I have prolems with Inventor. and Inventor has worked fine before for the past 6 months.
Showcase is easy to use and can generate nice looking results pretty quickly - I use it extensively rather than tweaking Inventor's materials (which, to me do not look even close).
I also see the same behavior you are describing when I switch from Showcase back to Inventor. It actually changes the option in Inventor for "Software Graphics" (Tools > Options > Application Options > Hardware > Software Graphics). So, you have to open Inventor, uncheck the Software Graphics checkbox, close Inventory, then re-open it.
It also resets the selected Project in Inventor each time I use Showcase. Little disappointed in the "interoperability" between the two applications, but once you get used to the song and dance you can be productive with the combination.
I've also tried using 3DS Max, but so far the learning curve has been steep enough that I've not made the switch from Showcase.
Check into Keyshot when you get a chance. I had the same issue you had with Inventor Studio. I personally think it looks terrible. I've attached a render I did of one of our mobile towers. I think it looks pretty real. Also Keyshot took me about 5 minutes to figure out how to use it and it also has animation capabilities. And if you were wondering, I have no affiliation with Keyshot I honestly just think they make a good product.
Is it possible to make the parts travel freely in Showcase or in Keyshot? In Showcase was only able to move them so that they travel to one direction and then the part would make "corner" and travel to the another direction. I don't have Showcase installed anymore so can't test myself.