Flashing orange light

Hi guys
I am wondering if someone can help. I have an old Dell Demesion 5051 desktop running on XP. I haven't up graded, because I only use it for art work and I need the old o solute programme Picture it and Presto page manager. I have never had any problems in over ten years, unti a few months back, when I tried to boot it. The signal turn on button just flashed orange and it would not boot up. I tried a few more times but nothing. Then a couple of days later I tried again and it started up. Everything was fine until last week, when the same problem occurred again. I kept trying to turn it on and off several times, eventually it booted and worked as normal.

It's just getting longer and harder to get it to boot. Someone said to change the bios battery and today I did, but it made no difference, eventually I got it started but now I have a press F1 to start or F2 come up and I hear two beeps on start up. I have turned it off and managed to restart it every time, several times in the last hour,but the above comes up each time. I am not even sure if it will start up tomorrow.

Can anyone tell me what the problem is...someone said I may need a new CPU box, whatever that is. I am 75 yrs old and was totally amazed that I managed to change the battery..but that's about it and my knowledge of computers and components are zero!

Thanks for reading, sorry it was so long, but I wanted you to have all the facts.