Hi Yazbekistan.
I will be able to assist you.
Please note that you have reached the forum for Canon USA and the i-SENSYS MF4780w is neither sold or supported by Canon USA. However, I do recommend downloading and installing the Network/USB Scan Patch. I have included a link to the download for your machine below:
Canon i-SENSYS MF4780w - Drivers
If you still experience an issue with the scanning function, we will have to recommend that you contact the Canon support group in your country for further assistance.