That is a very unusual situation. Have you ever
installed a version of
Windows, just to see if it does the same thing?

I use Ubuntu, not Kubuntu, (but they are not that
different except in the
default shell), and never had that problem. I really
question whether it is
an operating system issue... I suppose you have
checked your settings for
Sleeping and Hibernation?

The only time I ever had a similar problem was many
years ago when I bought
a computer which had a defect either in the memory or
the mainboard, causing
it to freeze several times an evening. The builder (a
small company) finally
fixed it but never told me what the problem was.