Why database is corrupted after re-booting

Yesterday  computer running Postgres re-boots suddenly. After that,

select * from firma1.klient

returns

ERROR:  invalid page header in block 739 of relation "klient"

I have Quantum Fireball IDE drive, write caching is turned OFF.
I have Windows XP with FAT32  file system.
I'm using PostgreSQL 8.0.2 on i686-pc-mingw32, compiled by GCC gcc.exe (GCC)
3.4.2 (mingw-special)

Why the corruption occurs ?  How to avoid data corruption?
Will NTFS file system prevent all corruptions ? If yes, how to convert FAT32
to NTFS without losing data in drive ?

Andrus.