How much free, clean, freshly defragmented space is on your C drive? In order for the program to operate, you'll need at least 20-30 gigs. And, particularly since you've got an older computer, it may be a good idea to run a program like Advanced System Care to get the junk and tmp files out.
If you are trying to rip the files to your C drive, you'll need even more free, defragmented space. Like about 10 more gig for every 15-20 minutes of footage you're working with.
If you are ripping to another drive, you'll want to make sure that drive is formatted NTFS and not FAT32, as they come from the factory. FAT32 drives have a file size limit that can choke video editing work.
Along with Steve's questions and observations, are you trying to Import directly from a DVD disc, or have you Copied over the VIDEO_TS folder and files to the HDD? The latter is by far the better, but obviously, will require some HDD real estate.
Scratched DVDs make it difficult for Windows to read the contents in them. PrE relies on what Windows sees and that could be a reason for the lockup. As Bill suggested, you can copy the vob files to the Hard Drive and then get them into PrE.