My Samsung Galaxy 3 (GT-i5801) is not being detected by my PC -- What should I do?

I have a Samsung Galaxy 3 (GT-i5801 ) Android phone. Currently, my phone is not being detected by my PC. Initially, when I purchased this phone, I was developing applications and I was able to run the applications on my phone. I have purchased a new cable as I thought the data cable may have been damaged, but that did not solve the issue. What can be the possible solutions or what do I need to check for in order to connect my Samsung Galaxy 3 to my PC by using a data/USB cable? I have Windows XP installed on my Dell Inspiron laptop.