My computer starts to shut down. I haven't used it in a week. I took the battery out and it doesn't power up unless the a.c. adapter is plugged in. I tried some of the steps of taking out the battery and powering on and off. When it tried to start again, it took me to my sign on and then shut down. I receive a message that Windows didn't load properly and that I should restart. I have down that but it takes me to the same place. What can I do?