Not sure what your exact problem is because I'm not there to troubleshoot, but I had similar symptoms, namely my keyboard did not work at the login screen. I use an Acer Aspire laptop. Below are the steps I took to isolate and eventually resolve the problem. I am typing this from that same keyboard so don't give up :)
1. Is the problem only at the login screen or is it global?
I logged in as Guest, which doesn't require a password and can be done with a click of a mouse. If you don't have a guest account set up, proceed to #3. After logging in, I opened notepad and exhaustively tested every key on the keyboard. In my case, Esc, F10, F11, and [ worked. I also found that applying heavy pressure to multiple keys inconsistently caused a random number of the depressed keys to work. These findings caused me to think more hardware problem, but I was reluctant to open up the casing on my laptop until I ruled out software issues.
2. Software vs Hardware?
As Guest, I went to Control Panel->System->Hardware->Device Manager to check the Keyboard Driver. It seemed to be working but I wanted to uninstall and reinstall it just to be sure. Unfortunately the Guest account did not have sufficient privileges to do so. I opened the onscreen keyboard by going to Start->Programs->Accessories->Accessibility->On Screen Keyboard. Using the onscreen keyboard, I typed out my password onto the notepad, then copied it. Then I went to Logoff->Switch User to return to the Login screen, where I pasted the password to get into my normal account. Note that you should use switch user and not explicitly logoff because the former preserves the clipboard contents and the latter does not. After getting into my account, I uninstalled and then reinstalled the driver. The problem persisted.
3. Checking hardware connectivity
At this point, it almost certainly seemed like a hardware issue. You should have someone with experience taking a computer apart help with the next steps. Use all precautions including unplugging the power source and getting rid of your body's static electricity by touching something metal frequently during the procedure below. By reading the description of the procedure, you agree to release me from any and all liabilities resulting from the procedure below.
I opened the casing to the front of my laptop and released the screws holding down the keyboard component. Sure enough, the ribbon (wire) connecting the keyboard to the motherboard was loose. I simply reinserted and secured the ribbon and put everything back together. This took about 10 minutes total. On restart, the keyboard worked. I did take grainy pictures on my phone, which I can email if you drop me a line: jyy2111@gmail.com. However, since laptop configurations are different, it would probably be more useful to consult a manual specific to your model.
Anyways, good luck. Let me know if this worked for you.
Jason
