I was having exactly the same issue on my personal PC, but not having the issue on my company laptop. So I did a little contrast and compare via Device Manager on both PC’s. Ultimately what I did is the following:
1. Download latest drivers (or in my case, copy drivers folder from working PC and drop in non-working PC). The folders are split up for Vista 32 & 64, W7 32 & 64.
2. Open Device Manager – you should have a device that says something to the effect of Android Phone with and exclamation mark next to it. Your phone has to be plugged in via USB.
3. Right click and select the Driver tab and click on Update Driver button.
4. Select - Browse my computer for driver software.
5. Select – Let me pick from a list of device drivers on my computer
6. Click on have disk, which brings up a file dialog box.
7. Select the following file from the drivers folder you copied or downloaded from Step 1- WPDMTPHW.INF
8. Select HTC MTP Device – this should be the only option and click Next button.
9. Continue thru the prompts, confirm and now on the Device Manager you should see Portable Devices – HTC One_M8 (or M7 - whatever) with no problems or issues. Also, you should see it in Windows File Explorer in the Computer section.
I hope this helps!