With only 2GB of total memory, don't install or run XFast ram.
Your windows pagefile is probably slowing your system to a crawl when XFast Ram is running.
You can verify this by running windows Resource Monitor from the Task Manager button and selecting the Memory tab in Resource Monitor.
Moving your browser cache, TEMP and TMP folders, and possibly your pagefile to the ram disk should speed up your system if you have 8GB of installed memory.
Your system should be stable if you buy a 2 x 4GB memory kit and sell your current memory to offset the cost.
Mixing different memory brands and or models is asking for problems with system stability.
It's safest to buy a memory kit that is listed in the Memory Compatibility List for your motherboard on the ASRock web site.
8GB of ram with XFast ram using up to 2 or 3GB (depending on your needs) would be ideal.