I recently with to Windows 7 and I am having

There is no problem with your operating system which is the Windows 7. You encounter a hardware problem with your USB ports. It's not with the drivers. Your usb ports maybe defective. Buy an expansion usb card.

Check in the device manager if power management is set up on the usb hubs. I think there is a checkbox next to 'Allow the computer to turn off this device to save power'. Make sure the checkbox is empty, otherwise when windows goes into power saving mode it may turn off the usb ports. Some devices cope with the ports going on and off, a lot of older devices can have problems that require them to be unpligeed and replugged in again.