|If this is for your built in touchpad, try connecting a USB mouse, and then disable the touchpad in Device Manager|
(E.g. RIGHT click on My Computer - Properties - Hardware - Device Manager - RIGHT click on the entry for the touchpad and Disable it).
If you have no problem with that, you probably have a hardware problem with the touchpad - you must replace it, or use a different mouse.
If you prefer touchpads, there are also touchpad mice.
You could try this, but it probably WILL NOT help.
Go to Device Manager (see above).
RIGHT click on the entry for the touchpad, select Un-install.
Restart the computer.
If you can't move the cursor, press the Alt-Ctrl-Del keys at the same time, then Alt and U at the same time, then press R to Restart .
Windows will load the drivers for the touchpad while Windows loads
If you need to login while loading Windows, if the cursor won't move, press the Tab key to toggle what is selected on the screen, use the keyboard cursor keys if you need to, press Enter, after you have typed a password if that applies. The cursor will be movable shortly after the desktop screen has loaded.
Try the touchpad.
If that doesn't help.....
Connect a USB mouse. Use that instead of the touchpad. (You MAY need to disable the touchpad too - see above - and enable it after you have installed the drivers for it - see below.).
Go to the Acer web site for your country, download the touchpad drivers for your model. If there are directions there about how to install those drivers, READ THAT.
Un-install the drivers for the touchpad in Control Panel - Classic View - Add or Remove Programs .
(If there are no drivers for it listed there, Windows was probably using generic PS/2 mouse or USB mouse drivers for it.)
Install the touchpad drivers according to the directions, Usually you run the download to install them,
DO NOT install the drivers for the touchpad if Found New Hardware pops up for the touchpad , unless the directions tell you to do that,
"I have an Aspire 3690 laptop with Windows XP Media Center Edition Version 2002."
Your laptop may have been made in 2002, and it probably can't be any newer than made in 2003. It would not be unusual for the touchpad to become defective after all this time.
" Windows XP Media Center Edition ("Freestyle", Available in July 2002)  This was the original release. Updates to this release added a number of features, including FM radio tuning. This release combined with updates is sometimes referred to as Windows XP Media Center Edition 2003. 
Windows XP Media Center Edition 2004 ("Harmony", Available in September 2003)  Windows XP Service Pack 2 upgrades earlier versions of MCE to this one.
Windows XP Media Center Edition 2005 ("Symphony", Available in October 2004)  is the first edition of MCE available to non-Tier 1 system builders. Among other things it includes support for Media Center Extenders, and CD/DVD-Video burning support.":