Sometimes it just happens, and I dont know why, during the screen freezed my keyboard and mouse unable to work well, so I had to force shutdown to restart. I use google chrome as my main browser because firefox extremely laggy for me.
My computer spec is, Intel Celeron dual core processor with 1.60mhz speed. 4GB of ram. Intel HD graphic card (intergrated graphic card) 13:10 running ubuntu 64bit (fully updated)
Thanks in advance.