Nvidia GeForce 405 Not Recognized By 64bit Windows 7 SP1

I'm running 64-bit Windows 7, SP 1 and recently had problems with Windows updates not installing (going back to August).Windows Fixit didn't work, but an HP utility did, which then allowed updates to download and install. However, after the reboot to complete installation, I got the dreaded NTLDR Not Found message. Managed to sort that out (not exactly sure what did it: making sure the boot location was set to internal hard disc and/or using disc one of a three-disc HP Recovery set that I created after a previous NTLDR issue). The problem I have is that one update did not install:

nVidia - Display, Other hardware - NVIDIA GeForce 405
Download size: 188.7 MB
nVidia Display, Other hardware software update released in March, 2012.

I've tried to download the driver directly from Nvidia but that fails too, with the message that I don't have an Nvidia GPU!I even lost the Nvidia control panel. I checked the Nvidia components in the appropriate system folder and discovered that they were set for Windows XP. Changing them to WIndows 7 made no difference. I manually ran the Physx application (clutching at straws from a knowledge base of zero) and the control panel loads up but when I run it from the task bar, I get the no Nvidia GPU message. There definitely IS an Nvidia GeForce 405 present. It worked before. At one point, Device Manager showed it as present, but I can't repeat that situation: under Display Adapters it just shows Display.Under Sound, Video and Game Controllers, Device Manager shows 4 Nvidia HD Audio entries, located in Location 0,1,2 and 3 (Internal High Definition Audio Bus). Did they come from the Nvidia GPU set up? And why four of them? How do I get Windows to recognise the GPU and install the new driver? I'm not sure if it's related, but I also can't get Media Centre to find my XBox 360 as an extender. The error message indicates that it might be a Sunbelt Vipre Firewall issue. I've tried to set local port access as firewall exceptions as per the XBox web site suggestions, but I can't work out how to set the 'system' entries (there is no application labelled System to locate). My Packard Bell netbook located the XBox at the first attempt (also 64-bit Windows 7 SP 1, running McAfee-based BT NetProtect Plus). Sunbelt Support were, sadly, no great help, as all they did was direct me to the XBox web site after a very long web chat interaction. HP Support utility also repeatedly failed to install the Ralink WiFi driver update, but it succeeded the other day and then I had problems with not being able to connect the PC to the internet via the wired ethernet connection to my BT HomeHub 3 running Infinity (via the BT Infinity Modem). WiFi connection worked, but not wired. That issue disappeared after a couple of days (no idea why), but every time I start the PC I get a BT Help Browser redirect window attempt to load but it fails every time and I have to end the task manually. Under Netwrok Adapters, Device Manager shows:

802.11n Wireless LAN Card
Microsoft Virtual WiFi Miniport Adapter
Microsoft Virtual WiFi Miniport Adapter #2
Realtek PCIe FE Family Controller
WAN Miniport (IP) Sunbelt Software Firewall NDIS IM Filter Miniport
WAN Miniport (Network Monitor) Sunbelt Software Firewall NDIS IM Filter Miniport

However, under the two Sunbelt entries, Device Manager indicates that "Windows cannot load the device driver for this hardware because a previous instance of the device driver is still in memory. (Code 38) You need to restart your computer before the changes you made to this device will take effect." Closing the entry yields "Your hardware settings have changed. You must restart your computer for these changes to take effect. Do you want to restart your computer now?" You guessed it: restarting makes no difference and the same messages keep appearing under Device Manager.