There's a very good chance that the system is damaged beyond repair. If the computer has a CD-R/W (CD burner) or DVD-R/W (DVD burner) installed, I suggest backing up critical documents and media and preparing for a reformat.
Once all critical documents and media are backed up, I suggest the following steps:
1. Download and install Spybot - Search & Destroy from
http://www.safer-networking.org/en/download/
2. Download and install Ad-Aware SE Personal from
http://www.lavasoftusa.com/software/adaware/
3. Run Spybot - Search & Destroy, click the "Update" button on the left-hand menu, install the latest updates, click the "Search & Destroy" button on the left-hand menu, then click "Check for problems."
4. Reboot the computer.
5. Run Ad-Aware SE Personal, download updates if/when prompted, click "Finish," click "Start," select "Perform full system scan," and click "Next." After the search finishes, remove all detected threats.
6. Reboot.
7. Repeat Step 3 until Spybot - Search & Destroy detects no threats.
8. Repeat Step 5 until Ad-Aware SE Personal detects no threats.
9. Download and install AVG Anti-virus from
http://free.grisoft.com/doc/2/lng/us/tpl/v5
10. Run a complete scan using AVG Anti-virus. Delete or heal any infected files.
11. Download and install Firefox 1.5 from
http://www.mozilla.com/firefox/
12. Download and install Spywareblaster from
http://www.javacoolsoftware.com/spywareblaster.html
13. Run Spywareblaster, check for updates, and enable all protection.
14. Install the following Firefox extensions:
NoScript:
https://addons.mozilla.org/extensions/moreinfo.php?id=722&application=firefox
Adblock:
https://addons.mozilla.org/extensions/moreinfo.php?id=10&application=firefox
Adblock Filterset.G Updater:
https://addons.mozilla.org/extensions/moreinfo.php?id=1136&application=firefox
15. Set the default browser to Firefox and emphasize the importance of your father not using Internet Explorer for web browsing.
16. Run Spybot - Search & Destroy, click the "Immunize" button on the left-hand menu, and click "Immunize" in the main panel.
If the machine is still inoperable after this process, then it's time to format the computer, re-install the operating system, and install the programs listed in the above instructions.