Windows XP Repair?

Whilst deleting some files using:-
C Drive properties/General/File Cleanup I received an error message
stating that I needed to insert my Windows XP disc as some files were
missing to complete the task.

pmj...

Yep, that's the SFC (System File Checking) & WFP (windoze File
Protection) stuff doing it's job.

Inserting the disk, just brings up the splash window on the screen with

pmj...

That's cos you have your CD Rom Drive Set (like most people do) to
"AutoRun" - it's just Running the standard "Welcome to windoze" thing
from the CD when you put it in.
Exit out of that (or hold down the Shift Key when you put the CD in,
to Stop it from AutoRunning) & then Click [OK] on the SFC/WFP Dialog Box

no 'repair' option.

Is there a way to repair Windows or check for missing files?

pmj...

Yep.
You can run the System File Checking Utility from a Command Prompt

start>run cmd [OK]
sfc /scannow [Enter]

& you can also do a "Repair" Installation of WinXP [*1], but that's
a bit drastic. You may not need to do that yet.

[*1]
By Booting off the Install CD & choosing
"To set up windoze XP now, Press Enter"
& then choosing the existing Installation on the Hard Drive - it will
tell you that there's already an Installation there & ask if you want
to do an "over the top" Install.

*Don't* choose the Option "To Repair a windoze XP Installation using
Recovery Console, Press R" - unless you want to use the (CommandLine)
Recovery Console. You would have to find out more about using the
Recovery Console, before trying to use it.)

Also, rather than doing a Re-Install yet, try System Restore from
the Accessories>System Tools Folder in the Start Menu or in the
Control Panel.