You should check the boot order that is set in BIOS. Power off your laptop, then power it on. Press F2 as soon as it starts to access your BIOS' settings.
Go to the Boot tab and select Boot Priority. Set your hard drive - where Windows and Ubuntu are installed - at the top of the list. Then, press F10 to save and exit.
Are you still facing the issue?
If yes, try looking at your BIOS configuration in Advanced > System Configuration > Boot Mode - you may set it to UEFI instead of Legacy (CSM Boot) or vice-versa. For example, if your Windows is installed in Legacy mode, you must install Ubuntu in Legacy mode as well and use the proper boot mode in BIOS.
Hope that helps.