BleepingComputer.com: Problems after upgrade to XP Pro SP3

In the course of recently trying to get rid of what was possibly a virus infection, I upgraded from XP Home SP2 to XP Pro SP3. There proved to be no virus after all but, by the time I discovered that, I had installed this probably irreversible upgrade and it has left me with several faults:

• standby and hibernate are dimmed out on the shutdown menu
  
• the display seems to be working in VGA mode and will not produce its former quality
  • scrolling in the browsers (IE8 & Firefox) and email client (Thunderbird) is not properly controllable (although it seems ok in places such as Windows Explorer)
    
  • the Windows screen fonts appear either too thin (and low quality) or too bold
  
  
• Device Manager states that there is a graphics card that is not connected.