Server not starting problem

Hi all, im very new to postgres, and im having a problem with postgres 8.1.

The thing is that the server wont start, when I checked the log it said:

Received fast shutdown request

Aborting any active transaction

FATAL: terminating connection due ti administrator command

FATAL: terminating connection due ti administrator command

FATAL: terminating connection due ti administrator command

FATAL: terminating connection due ti administrator command

FATAL: terminating connection due ti administrator command

Shutting down

Database system is shutdown

Logger shutting down

When I log into de pgAdminIII the server appears with a red cross, when I
try to connect it sais "server doesn't listen"

On the event viewer I have errors that say:

FATAL: syntax error in file c:/program
files/postgresql/8.1/data/postgresql.conf" line 435, near token "MB"

In line 435 of the conf file I have shared_buffers = 256MB

When I check the services running, I have the postgresql server stopped,
when I try to start it it says it started but stopped because it had no work
to do????????

Any suggestions? I would really appreciate it

Pablo