Inspiron n5110`

was getting 4 beep sequence continuous til login screen, beep cmos battery, changed battery with one , lost video but no beeps, troubleshooted, bad battery, replace with another new battery, booted fine, restarted 2 times worked fine, returned laptop, person did use the laptop for 4 days, they tried using it today and was getting 4 beeps, no video, power button stays on, wifi indicator comes on, but no harddrive activity. had them pull main battery, drain flea power, still no go 4 beeps no video.. why did it work more fine twice and after 4 days it doing same thing again