IE causes system to become unresponsive !

Hi Guys

have been finding this prob with my hp desktop , which is 512 mb ram, 1.8 GHz AMD athalon processor, with 80 GB HD. the problem is when i am surfing and if i open a lot of browsers (say about 8-9), then suddenly i cannt minimize or maximize or close the minimized browsers (i use IE). i also even cannt open any other application, the cursor keeps moving normal but if click on something to open it, just the dumbell appears for a second but nothing happens after that.. even i cannt open the program list by clicking on "Start".
please help me in solving this problem..

 

with that same ram i was using it from last 4-5 years, how come suddenly that much ram is not enough? could you please explain little more.. and is there a way to confirm that actually low ram is the culprit?
my laptop has same 512mb ram and works fine..

many thanks for the kind reply !