Dell 8200 XP SP3 Locked Lost APP Access

Problem with DELL Dimension 8200 running XP Home Edition with SP3 with all current updates.An old dog(PC) getting ready for the junk heap but right now is not the time.After installing Quicken 2010 and TurboTax 2010 and working in those Apps for a couple days, startup items stopped loading in the systray during IPL after I got three icons: the mouse, keyboard and my network connection to appear. Error messages were generated as follows:
Error loading NVQTWK Retro Express.exe.Application failed to initialize properly
RUNDLL
Error loading NVCpl.dll
Setup Error
Failed to load resource from resource file.Please check your setup.
These are only a sample but representative of the responses when clicking on short cuts to open apps.
Running Windows Defender (in Safe Mode with Networking) says there are no malicious or unwanted softare detected.When attempting to check for definition updates the following displayed:
Error Found: Code 0x8007043c.
Until a month ago had been using ESET NOD36 to keep me safe.Since then I'm using IOLO System MechPRO to do the same until it could not be accessed at the same time everything stopping working 4March2010.
Can access the internet in Safe Mode using Mozilla Firefox.Can't access Web at all in regular mode.
Ran Microsoft AutoPlay Repair Wizard in Safe Mode. It detected the Shell Hardware Detection Service is set to Auto Start, but when click on FIX to START it, the a Wizard could not restart it. (Tried this couple of times no start).
In regular mode tried switching between user accounts but keep getting message, 'This computer is in use and is locked'.