If you literally meant deadlocks - thats a whole different story (monitor the locking).

If you meant freezing up - You may want to set a min server memory as well (plus your max is too high as mentioned for an 8gb machine). We had an issue where the system cache was eating into the SQL memory if it wasn't in use, and then it wouldn't reclaim the memory when needed even with locked pages switched on. Small chance this could be your reason.

Keep an eye on the Target and Total server memory counters in perfmon (as mentioned) and the system cache counters too.