stop sign after manual install the update snow leopard

[FrenzyBanana]

i duno what to do now
after i install the update combo 10.6.5 my pc restart and stop sign appeared
now my imac is so useless

 

[Bernard SG]

Try to reset PRAM, first.
If not working, start your Mac OS from bundled DVD and check your HD with Disk Utility.
Hope you have a TimeMachine backup of your drive, you may need to re-install your system from the DVD.

 

[FrenzyBanana]

can i backup first before i re install my system?

 

[Bernard SG]

I don't get it. Is your Mac starting up?
Do you have an external drive?