CMOS battery

Few days ago, I heard a beeping sound with black screen when I booted my Dell laptop Alienware M17XR4. So, I forced to shut down the laptop and rebooted. After I booted my laptop, I noticed that my laptop calendar and time on right bottom corner got reset to factory condition which was "12:00 AM 1/1/2015". From then, the beeping sound and the black screen kept showing whenever I tried to turn on the laptop. So I had to force to shut down and reboot whenever I tried to turn on the laptop. I thought my CMOS battery died so replaced with new one. After I changed the CMOS battery, I do not see any problem to boot the computer and heard neither beeping sound nor black screen. However, the calendar and the time still got reset whenever I turn on the laptop even though I changed it to current date and time in BIOS and synchronized with Internet time server. I tried it about 10 times, but it got reset every time. So please help me.

Thank you.