Enable (Disk) Write Caching problem

Hi Geeks, I need expert advice.....again. This a summary description of the issues this time..

This built up from trying to test HDDs with HD Tune...
I get the error message 'Windows - Delayed Write Failed' when testing a slave HD on my IDE cable using HD Tune - Error Scan. The disk is recognised correctly in the BIOS as the primary slave and shows up in Windows Explorer OK. When using HD Tune on this disk I get unrepeatable results for scans. I have noticed also that there is seemingly a coincidence between the error Delayed Write Failed and HD Tune starting to detect bad blocks (once it has started it detects the rest as bad). I have installed this disk in the PC because I was experincing similar problems using it as an external USB disk. I have changed to disks always on in CP>Power to avoid any possibilty of any problem with the disks being turned off (I have found previously that this appeared to help with other disks).
I read in a microsoft KB article that this may be due to the disk having Write Caching Enabled, so I go to Policies for this disk and clear the radio button to disable write caching, and get ready to start. I notice that the disk temperature reading is not available and also that the temperature of this disk has disappeared from Speedfan; this makes me go back to Policies to see if I can regain the previous state, but I find that the whole Policies page has been greyed out, with Optimise for Performance and Write Caching Enabled buttons seemingly selected.

Please advise me on how I can overcome some of these problems.

Dumb_Question
17.June.2014
Compaq Presario S5160UK DT261A under XP/SP3
Processor - Celeron 2.7 GHz
Motherboard - MSI MS-6577 v2.1
RAM - 1GB + 512MB (1GB +1GB max) DDR PC2700
PSU - Octigen 300W model 10270PSOTG ('upgraded' from original Bestec 250W PSU [in 2011?])
Nvidia GeForce 6200 graphics card in AGP slot.