No Launch of Win Explorer etc.

[Stella]

For some unknown reason ( at least to me) my machine has suddenly stopped
responding to Desktop and/or Start/Program launches of Windows Explorer, My
Computer and certain other progs. Other apps like Word, Excel and IE are
fine.
For example, if I double-click on Windows Explorer via the Desktop I get the
*hourglass* up for about 5 seconds and then NOTHING.
Start is also a problem and launching it is a bit of a hit and miss affair.
When I do *get through* and look for Windows Explorer I cannot see it.
I've re-installed XP-Pro SP1 without any of the *recovery* options and find
myself in exactly the same situation.
Sometimes I manage to hit the right spot and get to right-click Windows
Explorer and then go to Properties where it shows me that *explorer.exe* is
located in *systemroot* (is this significant ?)
I had NAV installed but that now just gives error messages at boot-up. I'd
like to re-install it, and check out the machine, but without being able to
get to the CD via Explorer or My Computer that's not an option.

Any ideas PLEEZE

TIA

Stella

 

[Stella]

Further to previous posting - I've just noticed that :-

1) when I go to Task Manager the CPU usage is permanently at 100%
2) the clock in the Tray is still at the same time as when I booted-up .
Any significance ? and if so what.?

Even more frustrated-
Stella