MTP USB Device Failed

My Lenovo A3000 was working fine till it got infected with some viruses. I tried many apps like CM Security, Avast , Malware Byte but it did not help. So, I did Factory Reset. But after that I found that Google Play Store is not working. It gives a error massage "could not be downloaded due to an error 491". So, I again did Wipe data/ Factory Reset(pressing Vol up + Power button, U know how to do that I do not know the technical term). This time I get new problems like "unfortunately gapps has stopped working" and "android keyboard has stopped working aosp". So I decided to flash stock rom which i found in another post of XDA . But when I tried to install the driver to flash the rom i got another problem which was my computer did not detect my device I mean it was supposed to show a device like MTKxxx in device manager but it did not. When I switch on the Tablet and connected it to pc get another problem like "MTP USB Device Failed". So. it will be very much help if anyone can help me with anything. Thank you.:confused: