Calum
First thing to do would be to check in the folder where you saved the file and see what the file size is
If it isn`t a very big file then that would suggest a PC issue, ie not powerful enough, V29 does require quite a lot of computer resources.
If it is a very big file that would suggest that you have used many operations to create the 3D model, have a look at your "CAM Tree" on the left, the more operations in there then the larger the file will be.
If you are happy with the final Model then one way to reduce the file size quite dramatically is to copy and paste just the solid model into a new document and save that under a different name.
This way you don`t carry over all the operations in your "CAM Tree" so a much smaller file
You can then save the original if you want at the end of the day or work period just leaving the PC to save the original while you drive home, but if you are happy with the saved smaller file then you can just delete the original !!
If you have generated a lot of 3D toolpaths with very small DOC and Stepovers that will also make for a larger file, if need be do several files with fewer features in each file.
When working with 3D models the number of faces really bumps up the file size, for example creating threads or multiple grooves in a Model will greatly increase the file size, nice to show actual threads but if they are not needed for actual machining then they don`t need to be shown unless it is for presentation for the customer etc
Hope that helps a little
Regards
Rob