this occurred to me and i solved it.
really took me some time, so for anyone might need help.

i brought a new computer and tried to install steam. the install itself is good, but when i try to open steam, it always try to update and then pop out '[FATAL ERRR] Steam needs to be online to update. Please confirm your network connection.' but my internet work totally fine.

i tried many ways, reboot, reinstall, disable firewall, all failed.
and when i starting to give it up, i found my computer time and date setting is wrong. its time was set at 10 years ago. i sync the time, open steam again and it solved.

i know that's stupid story, but i believe there's someone as stupid as i am. so if you are looking for the solution of this error, go check your date setting.