Why my pc automatically entering bios mode, when turning it on

If your computer keeps booting to BIOS, the issue may be triggered by the incorrect boot order. Just go to check if there is an appropriate boot device available in BIOS. If you find it, set the disk as the primary boot option. If your hard drive listed under boot device cannot be found in BIOS, change this hard disk.

A problem with the keyboard will cause this problem.

It can be wrong BIOS setting just try to load DEFAULT SETTING and you will see. Or if you start up to BIOS do you have correct time and date ? It can be cache battery.