Solution to slow shutdown/very high CPU usage/low virtual memory/slowness in system/automatic shutdown of system

Sometimes the ago my system (desktop) started giving below problems:

-          Automatically shut down after running for some time.

-          It was very slow.

-          The temperature of core rises abruptly and system gets shutdown.

-          Some popup says that your virtual memory is very low.

-          Very high CPU usage without any application open by me.

e  If i want to shutdown my system it will take 10-15 mins

I googled and found lot of info pointing to hardware and windows service pack. I tried few of those but result was same. One fine day my system just denied booting up. I just started the system, CPU was running but nothing was visible on the screen. I thought something tragic happened for sure, may be problem with hard disk/mother board. I called up a hardware engineer and he suggested to replace the RAM. I purchased a DDR2 2GB RAM and now my system is just like new. Very fast, no temperature rise in core and just perfect. So, I suggest all, if you see any issue like the one I have experienced, have a look at the RAM.