How much free, freshly defragmented space is on your C drive? When did you last clear the tmp files from this drive?
Are you editing to your C drive or to another hard drive? Is this drive formatted NTFS or FAT32 (as they come from the factory)? FAT32 drives have a file size limitation that often chokes video editing.
Finally, what are you using as source video for your video project? If you are using photos, have you ensured that they are no larger than 1000x750 pixels in size, per the FAQs to the right of this forum?
Thanks for the quick responses! I'm off to read the referenced articles. Certain large still photos in my latest video may be the problem.
Even if PrE can handle large Still Images, they sap the resources in a big hurry. See this ARTICLE for more background, and tips on resizing in Batch w/ either PSE, or PS. Note: the article was written when SD material was the norm, and Video Frames were 720 x 480, or 720 x 576. Further down, HD Frame sizes are mentioned. Still, all of the theory still hold, but the max sizes went up for HD.