The driver detected a controller error on \Device\Ide\IdePort0.

Error from Event Viewer. This error registers every or twice a second.

The driver detected a controller error on \Device\Ide\IdePort0.

- <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
- <System>
<Provider Name="atapi" />
<EventID Qualifiers="49156">11</EventID>
<Level>2</Level>
<Task>0</Task>
<Keywords>0x80000000000000</Keywords>
<TimeCreated SystemTime="2008-05-22T12:25:34.420Z" />
<EventRecordID>1746723</EventRecordID>
<Channel>System</Channel>
<Computer>Home-PC</Computer>
<Security />
</System>
- <EventData>
<Data>\Device\Ide\IdePort0</Data>
<Binary>0000100001000000000000000B0004C004000000850100C00000000000000000000000000000000000000000000000000000000005100000</Binary>
</EventData>
</Event>

Problems I'm encountering:
1. Arial font disappears every boot-up. Everything that uses an Arial font will be italicized.
2. HDD diagnostic utilities won't work
3. Sometimes, the HDD LED will light continuously, but no signs and sounds of reading from the HDD. After lighting continuously, everything on the monitor will be gone and there will be a BSOD. The computer will restart by itself but will fail to detect IDE drives

System specs (attached)

Well it states a controller error in your first (or only) HardDrive

This can be:
Your HardDrive (sometimes you may notice that it's noisy, or clunking)
Your IDE data cable (can be just a faulty data cable to the HardDrive)
Faulty IDE0 port on Motherboard (you could try plugging it into IDE1 - where the CD/DVD is)
Faulty Motherboard (Oh dear, no comment)
Sometimes it can even be the CD/DVD drive causing the issue (try unplugging it from the M/b)

That's about all

Your HardDrive (sometimes you may notice that it's noisy, or clunking)
No, I don't hear it noisy.

Your IDE data cable (can be just a faulty data cable to the HardDrive)
Will try this

Faulty IDE0 port on Motherboard (you could try plugging it into IDE1 - where the CD/DVD is)
Will try this

Faulty Motherboard (Oh dear, no comment)
I would throw a bomb on that computer store

Sometimes it can even be the CD/DVD drive causing the issue (try unplugging it from the M/b)
Will try this

Thanks.

I knew that one would catch me out!

It doesn't have to be noisy to be faulty, as you probably know
Here are some HardDrive diag tests (even though you've tried anyway)