Dell Laptop Beeps On Start Up And Then Freezes?

I am having a major problem with my laptop (Dell inspiron 1520). The laptop starts up, whe the dell logo disappears I get some very quick beeps (there must be about 8 beeps in total). I then get a boot manager screen which shows windows 7 at the top, and windows memory diagnostic in the tools section at the bottom. When I press enter it goes to the password screen and then after entering the password it seems to boot up as normal. I can probably get 2 - 3 minutes use out of my laptop before everything freezes. From this point I cannot do anything and have to tur the computer off by the switch.This is all it does in a constant loop.I have tried everything I can think of but still the same issue.

A couple of weeks ago my daughter spilt a little water on the keyboard. I mopped it up but next time I booted it up again the beeping noises started on start up. I removed the memory stick from under the keybpard and noticed there was signs of water damage. I removed the memory stick and the beeps on start up continued every time I booted the laptop up. But everything worked. Last Friday I was browsing the internet and that is when everything frozeI have tried to restore to an earlier date but it won't let me complete the restore. I have run the various disk repairs that are offered when pressing F8 at the dell logo screen but to no avail (it doesn't seem to find any issues). I really just want to get my files/photos off and then try and reinstall windows but as explained my computer won't stay on long enough for me to be able to do anythingThe computer will stay on in safe mode, however, it will not load in safe mode with networking. Could it be something to do with wifi? Reason I say this is I have been reading various threads and this has been suggested as a possible issue for one person's similar problem.