I have an XPS 8500 case. I've upgraded the PSU and GPU to Thermaltake Litepower 550W and EVGA RTX 2060 respectively. However, when I boot up the pc, I don't get any signal from the GPU when I connect it via HDMI while I get signal using the on-board HDMI port. How can I fix this? Also, how do I know that the GPU is working? I bought it brand new from Amazon. Thank you.