not recognized

Hello, I put a rom in my phone and later I wanted to change it because I did not like it and my phone did not want to turn on, my computer does not recognize it .. I tried the basics to try to repair it but it did not work .. any help? I think the problem is because the pc does not recognize...

Every time I try to download something using Chrome or the original Internet browsing application - Browser, it gives me an error like it couldn't find any SD Card mounted, whereas I've got one inside of my device. Using latest xiaomi.eu ROM for this device. What is possibly the matter?