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I have been using 3G USB stick on my laptop which has Win7 64 bit installed. It worked fine for last 1 year and suddenly one morning when I tries to connect USB it said Please connect device. I unplugged modem and tried multiple times but system couldn't detect it. Then I looked into device manager and it showed yellow flag on device drivers for USB modem with below error:

Windows cannot verify the digital signature for the drivers required for this device. A recent hardware or software change might have installed a file that is signed incorrectly or damaged, or that might be malicious software from an unknown source.

I re installed device drivers but no success.

I Googled about it and only solution I found is press F8 while booting and then disable driver signing. Just wondering how it worked for 1 year and suddenly stopped working.

Note: Previous day I had changed some services and set start up type as Manual, I don't really know which all services I modified. Can this be an issue?

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up vote 0 down vote accepted

Since you have changed system services and don't remember which ones, you can try System Restore to set your system back to a point previous to the changes. System Restore can be found by going to START > All Programs > Accessories > System Tools > System Restore.

Typically one the latest restore points are shown. If you don't see a date before you made the changes, you may need to check the box at the bottom to see more restore points (see image below).

enter image description here

To answer;

Previous day I had changed some services and set start up type as Manual, I don't really know which all services I modified. Can this be an issue?

Absolutely it will be. You should not change services unless you know what they do and how it will affect the system.

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