Ok, I rebooted and...even from a fresh start I gets no GPU device.
So I reinstalled driver version 12.3 from the previous versions link:
http://support.amd.com/us/gpudownload/windows/previous/12/Pages/radeon.aspx?os=Windows%20Vista%20-%2...
And then the GPU showed back up. I have no idea how many minutes or hours the GPU device will be available, before it disappears again:
C:\Users\Keith>clinfo
Number of platforms: 1
Platform Profile: FULL_PROFILE
Platform Version: OpenCL 1.2 AMD-APP (923.1)
Platform Name: AMD Accelerated Parallel Proces
sing
Platform Vendor: Advanced Micro Devices, Inc.
Platform Extensions: cl_khr_icd cl_amd_event_callbac
k cl_amd_offline_devices cl_khr_d3d10_sharing
Platform Name: AMD Accelerated Parallel Proces
sing
Number of devices: 2
Device Type: CL_DEVICE_TYPE_GPU
Device ID: 4098
Board name: AMD Radeon HD 7900 Series
Max compute units: 32
Max work items dimensions: 3
Max work items[0]: 256
Max work items[1]: 256
Max work items[2]: 256
Max work group size: 256
Preferred vector width char: 16
Preferred vector width short: 8
Preferred vector width int: 4
Preferred vector width long: 2
Preferred vector width float: 4
Preferred vector width double: 2
Native vector width char: 16
Native vector width short: 8
Native vector width int: 4
Native vector width long: 2
Native vector width float: 4
Native vector width double: 2
Max clock frequency: 925Mhz
Address bits: 32
Max memory allocation: 536870912
Image support: Yes
Max number of images read arguments: 128
Max number of images write arguments: 8
Max image 2D width: 8192
Max image 2D height: 8192
Max image 3D width: 2048
Max image 3D height: 2048
Max image 3D depth: 2048
Max samplers within kernel: 16
Max size of kernel argument: 1024
Alignment (bits) of base address: 2048
Minimum alignment (bytes) for any datatype: 128
Single precision floating point capability
Denorms: No
Quiet NaNs: Yes
Round to nearest even: Yes
Round to zero: Yes
Round to +ve and infinity: Yes
IEEE754-2008 fused multiply-add: Yes
Cache type: Read/Write
Cache line size: 64
Cache size: 16384
Global memory size: 2147483648
Constant buffer size: 65536
Max number of constant args: 8
Local memory type: Scratchpad
Local memory size: 32768
Kernel Preferred work group size multiple: 64
Error correction support: 0
Unified memory for Host and Device: 0
Profiling timer resolution: 1
Device endianess: Little
Available: Yes
Compiler available: Yes
Execution capabilities:
Execute OpenCL kernels: Yes
Execute native function: No
Queue properties:
Out-of-Order: No
Profiling : Yes
Platform ID: 000007FED5202A08
Name: Tahiti
Vendor: Advanced Micro Devices, Inc.
Device OpenCL C version: OpenCL C 1.2
Driver version: CAL 1.4.1703 (VM)
Profile: FULL_PROFILE
Version: OpenCL 1.2 AMD-APP (923.1)
Extensions: cl_khr_fp64 cl_amd_fp64 cl_khr_
global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int3
2_base_atomics cl_khr_local_int32_extended_atomics cl_khr_3d_image_writes cl_khr
_byte_addressable_store cl_khr_gl_sharing cl_ext_atomic_counters_32 cl_amd_devic
e_attribute_query cl_amd_vec3 cl_amd_printf cl_amd_media_ops cl_amd_popcnt cl_kh
r_d3d10_sharing
Device Type: CL_DEVICE_TYPE_CPU
Device ID: 4098
Board name:
Max compute units: 4
Max work items dimensions: 3
Max work items[0]: 1024
Max work items[1]: 1024
Max work items[2]: 1024
Max work group size: 1024
Preferred vector width char: 16
Preferred vector width short: 8
Preferred vector width int: 4
Preferred vector width long: 2
Preferred vector width float: 4
Preferred vector width double: 0
Native vector width char: 16
Native vector width short: 8
Native vector width int: 4
Native vector width long: 2
Native vector width float: 4
Native vector width double: 0
Max clock frequency: 3010Mhz
Address bits: 64
Max memory allocation: 2147483648
Image support: Yes
Max number of images read arguments: 128
Max number of images write arguments: 8
Max image 2D width: 8192
Max image 2D height: 8192
Max image 3D width: 2048
Max image 3D height: 2048
Max image 3D depth: 2048
Max samplers within kernel: 16
Max size of kernel argument: 4096
Alignment (bits) of base address: 1024
Minimum alignment (bytes) for any datatype: 128
Single precision floating point capability
Denorms: Yes
Quiet NaNs: Yes
Round to nearest even: Yes
Round to zero: Yes
Round to +ve and infinity: Yes
IEEE754-2008 fused multiply-add: Yes
Cache type: Read/Write
Cache line size: 64
Cache size: 65536
Global memory size: 8581414912
Constant buffer size: 65536
Max number of constant args: 8
Local memory type: Global
Local memory size: 32768
Kernel Preferred work group size multiple: 1
Error correction support: 0
Unified memory for Host and Device: 1
Profiling timer resolution: 340
Device endianess: Little
Available: Yes
Compiler available: Yes
Execution capabilities:
Execute OpenCL kernels: Yes
Execute native function: Yes
Queue properties:
Out-of-Order: No
Profiling : Yes
Platform ID: 000007FED5202A08
Name: AMD Phenom(tm) II X4 940 Proces
sor
Vendor: AuthenticAMD
Device OpenCL C version: OpenCL C 1.2
Driver version: 2.0 (sse2)
Profile: FULL_PROFILE
Version: OpenCL 1.2 AMD-APP (923.1)
Extensions: cl_khr_fp64 cl_amd_fp64 cl_khr_
global_int32_base_atomics cl_khr_global_int32_extended_atomics cl_khr_local_int3
2_base_atomics cl_khr_local_int32_extended_atomics cl_khr_int64_base_atomics cl_
khr_int64_extended_atomics cl_khr_byte_addressable_store cl_khr_gl_sharing cl_ex
t_device_fission cl_amd_device_attribute_query cl_amd_vec3 cl_amd_printf cl_amd_
media_ops cl_amd_popcnt cl_khr_d3d10_sharing
