Urgent Laptop problem

I was attempting to add more RAM to my mother's laptop, but I noticed that I had purchased the incorrect type. After putting everything back together, the laptop would not boot. I've searched for solutions all over the internet, and can't find anything. The fan doesn't turn on, and there is no hard drive activity. I rechecked all connections that I am aware of, and nothing seems loose or out of place. I even removed the old thermal paste on the heatsink and added new paste. When I hit the on button, the power light is lit up, and heat is giving off by the heat sink. This is all that seems to happen. Any ideas?

I swear, over half the time that I post something here for help I solve it 5 seconds later. I tried reseating the RAM for the third time, and it booted like nothing was wrong. Thanks to anybody who read this.

You shouldnt have had to do so much to just get to the ram. Not the best idea on laptops to mess with the cpu for future reference as the pins on the cpu are very easy to damage ..... Just as a note though if you hot glue the mobo or reseat the cpu in future sometimes you need to leave the laptop overnight to dry as small amounts of moisture even from residue fingerprints can cause problematic booting ..

As a tip, when taking a laptop to pieces have a large piece of paper. Write on the paper where the screws came from. Make notes one the paper which part you've taken out in which order. Really helps when putting it back together. There's nothing worse than rebuilding a laptop and being left with a couple of screws and thinking "where the hell did these come from, i wonder if they're important?"

Anyway glad you got it sorted :D

Yeah I really shouldn't have had to go near the cpu, to be honest. Most laptops I've disassembled have required a simple panel to be unscrewed, but not this beast. Not only did the heatsink have to be unscrewed, so did the hard drive and keyboard... PITA.

Another handy thing to have if you can get one, is a service manual for the laptop.

I found my Inspiron 9400 free at a this site that has loads of laptop (and other) service manuals.

I seriously love happy endings when it comes to computers