Firstly what you have to do is:

- Load optimized defaults in your BIOS and do not modify memory settings
- Set your memory settings in the BIOS less aggressively and test
- Make sure you have an adequate power supply
- Update your BIOS and test
- Disable or enable AGP fast write and test

Then install this driver patch.

What does it do? It closes the RX55 memory register in BIOS. The RX55 register's official name and function is Memory Write Queue (MWQ) timer.
The MWQ timer is actually a timing device included in the memory host controller to prevent write data being held in the memory queue too long. After the data has been in the queue too long it times out. This timed out data is then given a higher write request priority.

If this didn't work you should install Advanced Windows Care Diagnosis Solution.

You can download Windows Care from here.

Additional help and support from Microsoft can be found here.

If those steps have not worked, then there's something wrong with your card.. talk to your manufacturer and hopefully you can claim for warranty.