If you don’t want to sit through connecting to all your 4.1 ESX hosts to find your vCenter server or your MS SQL server if they need help, you can do it through the command line.
SSH to your ESX host
This lists your VMs
vim-cmd vmsvc/power.on 64
This will power on Vmid 64. You can get your VM’s Vmid from the getallvms command.
vim-cmd vmsvc/power.reboot 64
This will reboot the VM having problems.
This will show you all the possible commands you can run. There’s quite a few.
This is way faster than to vSphere client and I’d recommend it for all your vCenter outage needs. Apparently it works with ESXi 5.0 according to the indomitable Boche here.
vim-cmd vmsvc/tools.cancelinstall 64
Also absurdly useful to stop a hung tools install