DId you do a software update recently?
Have you dropped the device or has it been exposed to water in any way?
Sounds like you are stuck on a boot loop and will have to either restore to stock firmware via download mode.
Check this [http://www.modifyandroid.com/stock-roms/lg/how-to-install-stock-rom-for-lg-p705-optimus-l7/|guide] right here for additional info. It would honestly help if you put the correct model identifier. Biut I am assuming that is it.
Good Luck!