Pls. Specify the firmware version. (Settings-> About phone -> Baseband version, kernel, Android version etc etc. Pls Specify.
Your latest software should be 2.3.6 Gingerbread DDLK1.
If not then update it using kies(Safe)
or Odin(It wipes all the data)
If still not or u hv the latest os, then go to recovery by switching ur phone comletely off and then press all the 3 keys together, home key, vol up key and power key until u see galaxy y written, then leave it. in that recovery touch screen won't work. u'll have to use the volume up and down key for navigation and home key for selection.
Choose wipe cache and data(Sry but u'll hv to format ur phone)