one thing you can try is using a different HAL for the machine during install. It's possible that the install is not working cause of the HAL it's using. To do this, press F5 when you see the "Press F6 to install 3rd part drivers" message. Select the Advanced Configuration and Power Interface (ACPI) PC HAL, and try installing that way.
There are a couple things that could be going wrong.
1. HDD. do you hear any kind of clicking or screeching coming from the machine?
2. PSU. These can go bad due to dust, but also due to time of use.
3. Memory. Dust can short the circuts on the boards, as well as heat over time can cause expansion that will break connections.
4 Dust. Look in the tower at the amount of dust in the case. Blow it out, outside with some canned air. You can use an air compressor, but you need to turn down the preasure on it to less than 15psi