Hi,
So, let's get the facts right:
- This is a windows 7 device
- It's a Desktop PC (so not a battery issue)
Before you continue, ensure you have a backup of your data.
- Method 1 Turn off automatic restart
- Hold down the Windows key and R
- A Run box will now appear
- Type the following into the box
sysdm.cpl - Press OK
- Go to the advanced tab in the new window that popped up
- Press the settings button under startup and recovery
- Uncheck "Automatically restart"
- Method 2 Clear dust
- As you mentioned, this device is incredibly old. There may be dust inside the PC, try cleaning out the dust
- Power Supply
- Try cleaning out and/or replacing the power supply.
Cheers!