postgres crash

Hi,

I am a complete newb with postgres. In fact, I don't even use it as such but have a problem with a crashed postgresql db associated with using Calendar Server on Mac OS X 10.6 on a Mac Mini. To cut a long story short, I had to reformat my hard drive and restore form a Time Machine backup. Now, when I try to start the calendar server, I get a crash message in the console log and some of the following in the postgres log. There are no dates / times in the log file so I don't know which entries relate to which activities - sorry!

FATAL: the database system is starting up
LOG: startup process (PID 313) was terminated by signal 6: Abort trap
LOG: aborting startup due to startup process failure
LOG: database system was interrupted; last known up at 2011-07-15 07:48:24 BST
LOG: unexpected pageaddr 0/2058000 in log file 0, segment 4, offset 360448
LOG: invalid primary checkpoint record
LOG: unexpected pageaddr 0/2056000 in log file 0, segment 4, offset 352256
LOG: invalid secondary checkpoint record
PANIC: could not locate a valid checkpoint record
FATAL: the database system is starting up
FATAL: the database system is starting up
FATAL: the database system is starting up
FATAL: the database system is starting up
LOG: startup process (PID 646) was terminated by signal 6: Abort trap
LOG: aborting startup due to startup process failure

I've tried using pg_resetxlog with the -f switch but I don't really know what I'm doing.

I've also asked the Calendar Server mailing list but have been requested to come to this forum....

Any hints / tips please?

Many thanks,

Matt