Running Windows 98SE.
On a normal boot, loads OK up to Network Logon. OK logon and the start-up sound effect plays and nothing else happens. Ctrl-alt-del shows that the anti-virus has loaded, but nothing else.
When loading in Safe Mode, you get the "running in safe mode" dialog. When you OK that, the taskbar displays very briefly and then nothing else happens.
Prior to this, I have run a registry clean-up program and was installing a program to optimise my Internet connection. During this installation, a dll was shown to already be in use, but I did not have anything else running so I ignored that dll. The installation needed a re-boot and that is where the problem above showed up.
Running in command mode is OK.
I have restored the registry from the day before, but no improvement.
I use the System Safe Gold software to secure most of the system files and dlls and have restored the files it secures.