After having my pc on for awhile,it starts losing some graphics on whatever screen that I'm using & whenI try to click on someting(example-"compose" or "send",or even just a drop-down window) it doesn't respond.Sometimes I will loose half of my "start" menu & can't shut-down properly because the "shut-down" part of the menu is gone.
When I try to use Ctrl,Alt,Delete, I get a message that comes up saying that my "resorces are dangerously low,would I like to terminate any of the following resources?"It will have different file or application names under that,(whichever applications that I've used) Then it has 3 little commands saying1) terminate 2)NO 3) cancel.
Once this window comes up I have to manually shut-down my pc.The problem is that it doesn't matter if I'm using my pc for 20 mins. or 2hours sometimes or if I only have 1 or 10 things open.It's as if my pc just decides to do this or not!
My pc is a compac presario,I'm running Windows ME,I use I.E.,& I have sbcyahoo DSL.I have 191.0 MB of Ram, & I'm only using 40% of my disk space. Does ANYONE have any idea why my pc is acting like this?

Firstly I would run a full virus and spyware scan on the machine.

Online Virus Scan - http://housecall.trendmicro.com/
Spyware Blaster - http://www.javacoolsoftware.com/spywareblaster.html
Ad-aware - http://www.lavasoftusa.com/