[TYPO3-install] Installing new extensions breaks back-end's CSS

[S PATEL]

I have a typo3 system which works mostly fine, however when ever I install a new 
extension the CSS on the back-end goes away, or seems to be parsed only partially.

Without the correct CSS, the usability of the back-end is severely diminished.

I've tried several different extension and they all seem to do this.

Typo3 version 4.4.6

If anyone has any ideas... all help is valued and appreciated. Ta!

_SP_