program problems PLEASE HELP

I have recently purchased a computer with windows vista. I am having problems
with programs such as winamp and itunes. After installing winamp i am able to
use this, but then after shutting down the computer and then loading it back
up, i open winamp and an error message appears saying "missing driver files
please re-install". After re-installing the program works although i became
fed up becuase i had to do this every time the computer started and decided
to switch to itunes. After using itunes for the first time I switched the
computer off, today i loaded the computer then loaded itunes to find an error
message saying "missing files please reinstall". Now im lost what to do,
PLEASE HELP

I have also found this to be the case for the pre-installed games such as
minesweeper.

I would appreciate if anyone can assist and tell me why these wont work.