Several days ago I went to start the machine and I got a message saying:" Operating System Not Found" I rebooted the system, press F5 and enter. Had to do this 2-3 time and finally started normally. For a couple of days it did this then day before yesterday and yesterday it started normal without doing that. I have cleaned it with the antivirus as best as I have been able to. I contacted HP.com thinking that it might be the battery but was told that my machine is obsolete. I can't afford to buy a PC right this moment. I will plan that early next year. Do you guys think that it might be a virus? It's very slow and it doesn't seem to have forgotten any other functions. Is it the battery failing? It's been 5 years since I bought it. I was told they do not have the battery for Pavilion 503N. What can I do any suggestions? I desperately wait for your help, and as always thank you so much for your kindness. Take care and have a good day!