Thanks everyone for your replies to date.
Pretoria - It's a desktop, but I have investigated power settings. They seem in order - I made them the same as mine (same OS and CPU). My machine's ok. His remains problematical.
Mazzy - I've checked the MS knowledgebase and found many references to shutdown problems, but none that deal with what this machine is doing - ie, after selecting RESTART it does the shutdown part of the cycle, but doesn't restart.
fobs - an excellent reference from your good self, as usual. I haven't read and digested all the possible links and off-shoots, but on skimming, it does not seem to address this particular fault. More reading required on my part when time permits.
The Restart Button on the keyboard and a "Restart" or "Restart now" button in any dialogue box, including XP's own Restart button in the shut-down dialogue, exhibit the same fault - the machine does the shut-down part of the cycle, but stops short of re-starting.
The PWR OFF and SLEEP buttons on his keyboard work as they should, so I think his keyboard and KB software is ok.
I'm thinking the problem may lie in a registry setting or BIOS setting (both not yet investigated due to lack of knowledge re the registry and I only just thought of the BIOS!!!)
Also, because he says it has been like this from day one of ownership, it could be a hardware (MB) fault, in which case he needs to sort it out with his supplier.
To give him a fighting chance, I thought I'd try to eliminate as many software and setting possibilities before he has to confront his supplier.
LL34 - It's doing the shutdown part of the cycle, so wouldn't that leave a "clean" machine for the restart pert of the cycle to deal with? ie, "restart" doesn't really have to deal with anything because all progs and processes are already stopped because the machine is already shut-down. CTRL-ALT-DELETE instantly commences a re-boot, whereupon the start-up process is quite normal.
Richard - Housecall reported TROJ_ISTBAR.F at C:\SYSTEM VOLUME INFORMATION\_RESTORE{very long string of hex numbers}\A0076694.EXE
I looked up Trend Micro's encyclopedia and found out what to do. As part of my own cleaning up process before I ran Housecall I had already deleted a few folders and files to do with a couple of porn diallers (teenage boys will be boys!!) from the root directory of the C drive and also from My Programs. (There were no uninstall options for them in Control Panel)
According to Houscall the file A0076694.exe is a randomly-named trojan set by a porn dialler. However, it is NOT a running process or application in Task Manager, so it's not loading, so I don't think it's an immediate threat, but I don't like it there. It seems to have gone into System Restore when XP set a System Check Point, would you agree? It would be better removed, but how do I do that from within the restore files? - those files and folders seem inaccessible. Housecall had a delete option for the file, but I didn't want to mess around with files in the System Restore area without seeking advice.
I tried a Repair, not to try to remove the trojan, but simply to try to fix the restart problem, but none of the administrator passwords my friend could remember worked, so I could not pursue that option.
Would an In-Place Upgrade (Re-installation) help, do you think? I've never done that in XP - would I have the same admin password problem as with Repair?
I've warned him about the possibility of a format and re-install, but I'm trying to avoid it in favour of a more diagnostic approach if possible, as much for my own education as his convenience.
TCS - I thought of that, but no, I don't think it goes to Standby mode because it won't wake up with mouse movement or keystrokes. Only CTRL-ALT-DELETE gets it going again.
Cheers all
AA