Hi
When I turn on my p.c. it starts to load up then half way through loading xp a error message comes up saying issas.exe.systemerror. And when I click OK on this box the p.c resets itself and does it again, is there anyway of sorting this please thank you

Isass.exe is a virus.
You need to boot into safe mode and run a FULL antivirus scan.
Here's more info

Thanks. I'm not to up to date with this stuff. So how do you enter safe mode

Boot up your computer as normal and just as it shows you the XP splash screen hit F8 repeatedly.
After a while it will give you the option to enter various Safe Modes.
You want the Normal Basic Safe Mode, this will become apparent when you get the list.
Go from there.
Please remember to read any messages you get and act accordingly.

Thank you very much. I'm trying that now. I got miistaken it is lsass.exe.system error message. Does that make a difference thank you

Either way a full AV scan will help.

There are a number of viruses around that name themselves as isass and Lsass.
Lsass is an important windows component, located in c:\windows\system32.
Sometimes these viruses write themselves to c:\windows NOTE: NOT in system32 folder !

I've entered the f8 option and tried to run on safe mode by selecting the option but it just comes up with the ame error message and in the box it is saying 'object name not found' this may be asking a bit much any chance of a step by step in what to do. I feel like throwing the thing out of the window, thank you

Sounds like a system repair maybe in order.
A system repair is relatively easy operation to do.
Just a case of booting to an XP CD and following the install path. Just before it starts reinstalling there's an option to do a repair (NOT recovery console).
Select this and it will rebuild XP without looseing any of your personnal settings and data.

For this option to work you need a normal XP CD, NOT a recovery disc as this WILL wipe your system

Thank you. So basically I have to load in my xp disk then let it run, if so I've already done this and it still does the same thing. Thank you

Yep that's basically it.
Here's some easy to follow instructions.
This one has easy to follow screen shots.

** Very Important **:
A recovery disc WILL completely delete your current setup and reset it to factory settings. You need a "normal" XP disc for this to work.

You are a star. Thank you very much looks like I have it running. Thank you