First, why upgrade.

Recently I discovered strange problem -- my RB450/MRT ROS 3.19 freezed without notable cause (had opened winbox window, nothing was logged, nothing suspicious on network interface load graphs). Sometime it works 20-30 hours w/o problems, sometime 10 mins. The only thing I changed recently is OS on home computers: win xp to win7. Tried to turn off any w7 network features (like ipv6 and all that), no torrents, etc -- no effect. Just random freezes.

So I decided to upgrade ROS to 3.23, downloaded it through torrent and FTPed essential packages to RB, then hit 'restart' button on winbox. Time pass, NIC LED flashed (eth5, then eth4, eth3,.., eth1/poe), then I hear one 'beep' (slightly longer than usual 'system starts to load', but maybe I'm wrong about that), and that's all. No 'twice beep' as usual, no IP connectivity on any interface (including eth1/poe that I leave untouched since bought, except turning off neighbor feature), nothing.

I haven't null-modem cable right now, so I can't connect to the serial console.

I can't connect through winbox by MAC address.

What do I do now? Any early suggestions? Except for nullmodem cable, will try to find one tomorrow.

Also, what exactly does 'reset' button? Tried to press it, nothing happened. Tired of doing every reboot by unplugging power cable.

You mean hit System Reboot button?
Download and run Netinstall on your PC,set Boot Server enabled, set IP in same network like your PC
http://www.mikrotik.com/download/netinstall-3.23.zip
Plug LAN cable to RB ether1 and PC LAN card and turn on RB and look for active Routers.
If something wrong with RouterOS RB always try boot over etherboot

Configured pc lan ip to 192.168.0.10, connected it straight to rb eth1/poe port, launched netinstall.exe, hit "Net booting" button,
[x] Boot Server Enabled
Client IP Address: [192.168.0.20]

powered up rb, waited few minutes.. nothing new in "Routers/Drives".

Found F/F serial cable;

RouterBOOT booter 2.16

RouterBoard 450

CPU frequency: 300 MHz
Memory size: 32 MB

Press any key within 2 seconds to enter setup..
loading kernel from nand... OK
setting up elf image... OK
jumping to kernel code
Kernel panic - not syncing: No init found. Try passing init= option to kernel.

How do I "pass options to kernel", as boot process suggested?

Also on workstation with multiple NIC, do NetInstall automatically chooses right NIC according to "Client IP Address" setting?

Also on workstation with multiple NIC, do NetInstall automatically chooses right NIC according to "Client IP Address" setting?

it doesn't care about IP addresses, it just looks for nearby Netinstall servers connected via direct cable connection.

make sure you "press space" when it asks, to enter the bios setup. set it to boot from network. you can't pass any options to kernel, it's just a debug message

No, I mean NetInstall server -- does he broadcast himself on all workstation NICs? Or chooses just one?

I think all

No, I mean NetInstall server -- does he broadcast himself on all workstation NICs? Or chooses just one?

hi
I think for using the netinstall you should have a nullmodem cable because you have to choose first boot device from that.

also, tu be sure, you can temporary disable all the rest of interfaces for the install.