You'll have to explain what you mean by "distorted" and "garbled".
Can we seen an example, please?
That's almost certainly an indication of a hardware problem, Russell: failing RAM; a dying hard drive (that's what it was when it happened to me); faulty card reader; damaged USB cable - any of these can cause what you're seeing.
It's implausibly unlikely that Lr is causing this: Lr makes no changes to a Raw file's data on import (it can write to metadata, depending on settings) but for the most part, Lr imports files completely untouched, and so - logically - it can't be "corrupting" the files.
Lightroom does "stress" hardware (especially RAM, and 4gb isn't a lot of RAM for Lr to work with), so that'd be my trouble-shooting starting point.
Some light reading here:
Thanks for taking time to provide the info above. I'm hoping it is card reader as that is the easiest to fix. The RAM level is a bit light but my plan has been to use this computer for travel - quick review of pictures, looking for keepers to be loaded on my higher RAM, larger HD, iMac at home. I did try two different SD cards with the same result so that is not the problem.