If your using an older graphics card or driver, GPU functionality in Photoshop may be limited or not supported.
Generally, consider using GPUs with an Average Ops/Sec of 2000 or higher on PassMark's GPU Computer Benchmark Chart.
If you still face any issues with Photoshop while using this GPU, please checkout the steps mentioned here: https://helpx.adobe.com/photoshop/kb/basic-troubleshooting.html
Thanks,
Akash