M1530 Heatsink Repair

I have an older XPS M1530 laptop that has only been used in the past 3-4 years. The fan seems to always run - and loudly - so I didn't use it much. But now I need it. I followed the advice in this blog and cleaned the cooling fan and replaced the thermal compound (Using Artic Silver 5). But when I reassembled, and tried to power on the computer will start for about 2-3 seconds, and then just shuts down. Any idea what I've done wrong?