My lock screen on galaxy 5 won't come on. It goes straight to home screen. Why is it doing that? It was fine 2 days ago. How can I get it back?

Three Reasons Why Screen Lock is Gone
1. Screen Lock has been deactivated (Instructions how to activate are at bottom.)
2. Android Screen Security File may have been deleted, and screen lock option is no longer on your devise.(A Factory Reset will restore original Android files)
3. Malfunction Somewhere in Samsung Phone. (A Factory Reset might work, but not guaranteed)
(How to Factory Reset phone at bottom.)

How to ativate Screen Lock and Security settings

1. Press the apps icon, it usually at the bottom of screen.
2. Find Settings and press that button to open settings menu.
4. Scroll down the menu to Lock Screen and Security, press that to open options menu.
5. The first option at top is Screen Lock Type.Press and Open.
6. You will have 3 lock types to choose from. Swipe Lock, Passcode Lock, Password Lock
(advise, do not forget password, only a hard phone reset, or an apk lockout file will get you back in)

If activating screen lock through settings did not work, or if option is not available, you can try to reset phone to the way it was when you bought it.

There is a couple things you should know.
1. contacts, photos, videos, downloaded apps, games, and everything not on the phone when it was first bought, or when you first got the phone will be erased.
2. You can back up contacts, photos, videos, in settings menu, scroll down to Backup and Reset. Or save to an sd card, and remove sd card before applying reset option
3. If you have an account (google or android email) associated with your phone, you will need email address, ([email protected]) and password to get back in phone after phone resets and turns on.) Dont remember password, Please create a new password now before continuing to reset to manufacture settings.

Reset Phone to Manufacture Settings
1. Remove SD Card, or its saved files will be erased.
2. Open apps, Open Settings Menu, Scroll Down to Backup and Reset.
3. Scroll down to bottom of page to Factory Data Reset.
4. Follow instructions to reset phone.

When your phone comes back on, Swipe Screen Unlock should be active at phone turn on, if screen lock is not showing try again to turn on in security settings.
If still does not work,
I am sorry, Your phone has permanantly malfunctioned. You can try your phone store, or a phone repair shop.