I did force shutdown on my MacBook Pro (2006 year, 15.4"), so, when I tried to boot, it shows apple logo (as usual) and shuts down. When I booting MacBook with Option key pressed it shows lock icon and field for password. Please help me.

Welcome to the Apple Support Communities

You have got a firmware password. If you want to reset that password and you don't remember, take the computer to an Apple Store. You will only be able to boot into OS X

When you had Snow Leopard on the machine you must have set a firmware password.

Stick in your original Snow Leoaprd disk and hold the option key and boot the machine, you can select the Snow Leopard disk to boot from and under the Utilities menu on the Installer screen is Firmware Reset.

http://www.thexlab.com/faqs/disablefirmwarepwp.html

If you can't remmeber your password, then you will need to take the machine to Apple to reset it.

Take your Mac to any reseller

Well you must have purchased a stolen item if you didn't set a firmware password.

We can't help you, but perhaps if you search online there might be a method to bypass the firmware password.