Dell OptiPlex 990 USB

And I take there's no "!" in a yellow triangle in Device Manager?  Just in case, do you have a different keyboard and mouse you can try?

It's likely the MB, but those are things I would look at first before MB or PC replacement.  MB's for the 990 are likely cheap with it being a little older.  If you go that route, be sure to get something for a return policy on it, like at least 30 days.

Yes! All drivers installed there isn't any "!" in device manager form Dell Driver Support.

I am using Logitech USB mouse and keyboard it is in a well-working condition. Tried with a different I/O devices and a USB system won't detect it. In fact, installed fresh windows and drivers.

I purchased this machine(used) from a local computer shop it was working for more than a year one by one found out ports aren't working. Maybe the's some issue with the MB.

Well, I was a Dell fan but the number of time tried to contact their support it is phatic they won't guide. Long story short as its a used system needs to get it transferred on to my name and then they are going to guide. When I try to fill the transfer form they need previous owner details &%^$ where I am going to get that form number of times to fill that form with the "No previous details" "Computer shop name" etc but that transfer process gets Denied.
Dell won't guide me out, its such a precious system for them. I wish could gift this same system keep it as a decoration.

Welcome to the Dell Community @ali ejaz 

Go to "Device Manager" and scroll down to "Universal Serial Bus controllers"

You should have 2 listed!!!

Intel 6 Series/C200 1C2D and 1C26:

Do you see them both and what version OS are you running???

Best regards,

U2

Yup! I have got these two (Intel 6 Series/C200 1C2D and 1C26) installed (image attached)
Renesas USB 3.0 Card: I am using that to use I/P devices
O/S: Windows 10 Pro 64-bit (10.0, Build 18363) (18362.19h1_release.190318-1202)

At last, got it fixed!!!

On a friend recommendation, yesterday went to a local electronics repair shop. That skilled guy traced out this issue was due to bad SMD ceramic capacitor.
Replaced that and its working now.

At least there should be some notification this is the issue it is showing all drivers are installed and everything is normal.

Glad you got it working.  Thanks for the info.  I'll have to remember that.

it would have been helpful for the sake of posterity if you would have elaborated on what a "SMD" ceramic capacitor is/does.  Your limited reply is not much benefit for future searches with similar problem.

The moderators of this forum didn't do any favors, either, in that regard.