Firstly it is worth saying that there could of course be a physical reason why this is not working.
However, normally when an SD card is inserted in a laptop I believe it to be recognised as a drive and assigned a drive letter much the same as a USB stick. This is normally linked to a message popping up on the screen in Windows XP or Vista asking you what you would like to do, and I think at least in some instances there is an option to say don't present this message in the future. This I think is what might have happened in your case.
If you venture into Windows Explorer can you see the drive letter of the SD card in the directory tree / structure normally displayed on the left hand side of the screen? If necessary select 'My Computer' and you should see C:, D: etc. including whatever drive designation your SD card has been given. An easy way to try and determine the drive letter of the SD card is to first of all view 'My Computer' with the SD card removed, and then to view 'My Computer' with the SD card inserted and there should be an additional drive designation displayed.
If you can see the SD drive letter in Windows Explorer then by right mouse clicking on the drive letter and selecting properties, and then left mouse clicking on the 'AutoPlay' tab, there should be a selection that can be made which reads 'Prompt me each time to choose an action' and by selecting this the presentation of the message when you first insert the SD card should be restored.
If instead however you cannot see the drive letter of the SD card in 'My Computer' when the card is inserted, this could be suggestion either a physical fault or a driver issue with the SD-reader.
Please try the above suggestion first before we look more deeply (possibly unnecessarily) into this problem.