Hope you're still around - the site is back up now.
In order for you to load Memtest at startup (bootup) you may need to change the boot order in BIOS. Make the order to be either floppy drive or cd drive - depending on what you have put Memtest onto.
Download - Pre-Compiled package for Floppy (DOS - Win)
Read the instructions on the web site.
You could leave it running over night if you wanted, I would run it during the day though - to keep an eye on things. Plus I prefer to shut everything down at night.
You will have to read instructions carefully to install on a CD or floppy, then boot with the disk in place. Let the test run for a few passes to be thorough.
If the Plug and Play service is disabled/turned off this can happen.
To turn the Plug and Play service back on, do the following:
1. Click Start - Run, type services.msc and click OK.
2. Double-click Plug and Play. If you receive a configuration manager message then click OK.
3.Switch the Startup Type to Automatic, click OK, and then restart the computer. You should be able to see your devices now listed in the Device Manager.
I can't help you on Incredimail, you seem to have done everything I would have suggested already. You could try uninstalling with Revo Uninstaller, might get a more thorough job - for a start it will identify anything left behind in the registry.