there is a very easy reason for this that for saving the memory the oracle is locked.
the solution for this is:-
1- goto control panel.
2- then switch to classic view(if it is at category view).
3- then go to the administrative tools>services.
4- then click on standard at the bottom(if it is at extended).
5- then search it the oracle.
6- then right click on that. then click start or restart....