Igor Vysoc you did not tell us if you removed those boards. If you did, post some pictures of those with your QUESTION. [guide|21499]
It is always best to remove and to properly clean everything with some high grade isopropyl alcohol. For a proper cleaning, use this guide. [guide|5825] It was written for a Apple iPhone 3G but it is still pertinent to your mouse as well. Truly assess the damage. Look for major corrosion, evaluate the pins in the connectors etc,. Take a look at all connectors as well as cable ends. Once properly cleaned, REPLACE THE BATTERY and reassemble to re-evaluate.