If you are receiving weird error messages upon startup of photoshop or if the loading sequence only goes so far and then just quits without reason, then there is a probable chance that you have problems with having too many fonts installed.
I'm not aware of any maximum number of fonts that should be installed, but if you are one that has many fonts installed then you should invest in a type manager to only load in the fonts that you need to use. There are so many fonts out there and many are so similar that many aren't needed and sometimes a font can become corrupt and then trying to find a problematic font in a list of 500+ fonts can be a nightmare.
Font Manager (Submitted by: kylebellamy) A recommended program for font management is Extensis Suitcase. This program is available for both PC and Mac and it allows the user to temporarily add and remove fonts from the system as needed.