Cannot find operating system. I have an emachine I purchased in 2000 which has given me great

Question

I have an emachine I purchased in 2000 which has given me great service. In recent months it has been having trouble getting started and the difficulty has been increasing. It has a Samsung 15GB Hard-drive. I found that cooling the PC in the fridge enabled me to get it to start most times. In the past 2 weeks it has become much more difficult. On some days I have been able to get it to start. On other days I have not. When the system searches for the hard-drive it seems to stop the search too quickly. When it does find it it takes 10 - 20 seconds. When it does not it says so in about 1 second