Vanishing pattern

 From:  Tom (TOMKIMBROUGH)
2472.1 
Hi Michael,
I am having a problem with parts of the model vanishing when I start turning it, and the pieces vanish from the model completly. I am running the following,
AMD Athlon 64x2 Dual Core 6000
3.6 GB Ram
ATI Radeon HD 4800
The size of the file is about 4 MB
Hopefully I am supplying the right info for you
Thanks
Tom