I have the same laptop, and I had the same problem as you.
If it isn't fixed for you now, you should also notice that when you try and Alt-Tab, it closes before you can choose the program you want to go to. Also when you try and log in to some online games, it types the = sign every second.
This is a BIOS issue with the Dell Inspiron 1501 laptop. To fix it, you need to update to the current BIOS version. As well as this, you should shutdown the laptop, unplug it from the back, take the battery out and hold down the power button for about 3 seconds, 3 times. Also unplug the power box from the lead that goes to the computer (you know, the plug in the wall goes to the adapter box)
Put everything back together, and the problem should be gone, and you'll be able to play the Sims 2 in peace.
The BIOS update also addresses the issue some users get where the computer crashes to a stripy screen. I got that a few times as well before updating.
I hope this helps you and anyone else with this problem.