It sucks when you can’t start or boot your android phone because your forget you password or pattern or might be your phone is lagging then its best to hard reset your android phone by using recovery mode and remove all your user data. You might need little different way to hard boot your phone but still its almost same on every android phone so check small tutorial below.
To hard reset your phone first make sure to switch off your phone by pulling out the battery. Then press and hold Volume Up + Volume Down + Power until you see the new recovery mode boot. You might need to use different buttons for different manufactures like Volume Down + Power for HTC, Volume Up + Power + Home button for Samsung galaxy or search on Google for your phone if this method not work.
Then press Volume Up or Volume Down to navigate through the options and select Recovery mode by pressing the Power button. As your phone will reboot the Android logo with red triangle will appear. After hold on the Volume Up + Power button until you see the new recovery mode options.
Make sure you have backup if not still you need to wipe all data through factory reset but don’t worry it wont delete any thing on memory card or contacts on sim card. If you confirm that you wanna remove all data then navigate to wipe data/factory reset option through volume buttons and select it by using Power button. Then Select yes delete all user data again through Power button.
I hope this small tutorial will help you to recover your phone and its best method to solve your lagging problem or if you forget your password. If you want to check few other android tutorials then go here.