Vostro 3750 - Strange USB Problem - Restarting attached USB flash drive every 5 minutes on its own

Hi I am having the above strange problem that started only a few days ago. Before this, it was working perfectly/normally.

My USB setup:

1) 4 port (self powered) usb hub connected to usb 2.0 port

2) another 6 port usb hub (ac powered) connected to the 4 port usb hub. this one has logitech unifying adapter & a usb adapter for calculator attached, with 4 empty ports free. Free ports mainly for flash drives, etc.

3) everything connect without problems normally.

A few days ago, whenever I attach a flash drive, the drive would disconnect & reconnect at an interval of 5 minutes. When it reconnects on its own, windows explorer will open to show contents of drive. This drives me crazy!

I tried the following fixes but have been unsuccessful:

1) tried going to Device Manager and turning off the "allow the computer to turn off this device to save power" - not successful.

2) tried different usb ports - not successful.

3) tried connecting 6 port usb hub directly to computer's usb port (without connecting to 4 port hub) - not successful.

4) tried method no. 3 on a different usb port directly on computer - not successful.

5) tried a brand new usb hub using methods 2, 3 & 4 - not successful.

6) tried connecting the flash drive(s) directly to computer (without hub) - not successful.

7) tried using different flash drives(s) using methods 2, 3, 4, 5 & 6 - not successful.

8) reviewed my windows update; I updated only the Office 2013 updates components on 16 Oct 2015 and everything was working fine. Have not done any windows security updates yet. Therefore I don't think the Office updates has any effect on this problem.

All of a sudden my usb port/hub seems to have a life on it's own, resetting/restarting in intervals of 5 minutes! I don't know what to do. Please help!