no more possible to repair the computer - windows vista

Concerns windows vista home premium sp1 installed on a Toshiba Satellite
A100-819.

The operating system is working normally, and also all installed software
works fine.

But it's no more possible to:
- use windows update: after a while there is a message that no updates are
possible. I have installed a program from Microsoft for 'auto' installing
updates, but no help.
- install extra software: at the end there is always an error
- install windows vista sp2: i have downloaded sp2, but i get an error by
trying to install

I have tried safety mode, stopped antivirus: it doesn't help.

All the old restore points are gone.

I have tried with F8 by starting the computer and 'repair your computer':
after 'loading files' i get an error: 'the installed program cannot be
started'.

I have no recovery cd/dvd for the moment of the Toshiba laptop (de cd is in
another country).

Can anyone help?

Hugo