The usual questions.
Service Packs and Hotfixes?
System specs?
Can you reproduce with any assembly, the Tutorials for example?
Is this a new problem, did it work previously?
Can you attach the assembly here?
Sorry, I'm pretty new to all this so I'm about to ask some pretty dumb questions, but what do you mean by Service Packs and Hotfixes?
I'm running Windows 7 64-bit with an Intel Core i7 CPU ~ 2.7 GHz and 4096 MB RAM. I hope that information helps.
Also, what do you mean Can I "reproduce" with any assembly?
I've never tried to render before, so I don't know if this is new or old.
I can't attach my assembly file because it keeps saying it's too large, even when zipped.
Periodically Autodesk releases Hot-Fixes and Service Packages to fix known problems with the software, (much like Microsoft does). They can be found here: http://usa.autodesk.com/adsk/servlet/ps/dl/index?siteID=123112&id=2334435&linkID=9242019
It's considered wise and prudent to check this location for Hot-Fixes and Service Pack's and install them.
Your system spec only shows 4Gb of memory for a 64 bit O/S. This would equate to having a 32 bit system with only 3Gb of memory. I would really look at adding/increasing your system's memory.