Machine can't work

Hello,i have a dell inspiron 8000,piii 1ghz ,256mb ram, after installing win xp sp2 the machine could not boot, after switching it on the hdd spinning but two lights comes on and beep twice and shut down. Sometimes boots up fine but after loggin comes up with an error message complains of the memory could not be read. sometimes goes to an extend of open folders then brings a message windows had a fatal error and its shutting down.
Please could someone help me solve the problem??.