Problem solved - it is due to the image size.
Both PCs are set to 1280 x 1024 and in the cache file settings the program is set to 240 x 160 for thumbnails which is the smallest option on the drop down box. When started up the size slider at the top of the display is set at the 50% position.
On the problem PC I moved this slider to 25% and the flashing stopped and the cpu cycles in TaskManger dropped to zero.
I have since imported more files - set tags and generally played around without any problems. The program keeps running and does not consume many cpu cycles.
When I stop and restart the program the 25% slider position is retained and everything works OK. If I increase the slider up to 50% the problem of flashing and excessive cpu resumes and then stops if I lower the slider again. The exact position of the slider varies but the problem kicks-in between 40 - 60%.
I am happy with this because my choice of size would have been 120 x 80 anyway but it was not available in the settings menu.
Thanks for your help. I am glad you solved this because your program appears to be just what I was looking for - a simple cataloging and sorting application without image editing bells and whistles and also allows me to keep my own folder structure.