Desktop running on windows xp home. When switching on, it freezes almost immediately. Problem? Computer is a hybrid of bits put together two years back - not by me, so unsure of exactly what's inside. I suspect my daughter has been switching it off at the wall....

Mick Dodds, October 2007

Ok, lets give you some practical advice. If switched off at the wall often your pc will have some corrupt system files. If indeed it does switch on, get yourself a Windows CD, boot to the CD and when presented with the options select the recovery console. Leave next option, default keyboard layout to select itself, then select 1, most commonly seen as c:windows. If asked for a password just press enter.It will make sense when you do it. Now you should have the c: prompt on the screen. Type chkdsk /r then press enter. Leave it as long as it needs - sometimes hours then when it is finished type exit and press enter. If you can do that, try your computer again and if it will not start come back here and we will try the next stage fix.

Scott H, October 2007

A few questions for detail:
Does it reach the windows XP logo with the moving blue bar below? (or even where the white bar goes across the bottom of the screen)
If yes, and it stops here, it is probably due to a corrupt or missing file within the windows directory. Use your windows xp disk to repair or reinstall windows. If you wanted an automated repair, ask it to install windows and it will then detect you already have windows installed and ask you if you want to repair it. If this repair process fails (the repair process shouldn't damage any of your data, but may disrupt some programs). There are many websites with in depth advice on t his which I have not got time to repeat here) If the repair process fails then a full re installation of windows will be required. Depending upon the options chosen this can remove all the data from your hard disk. If you have enough space on your hard disk, you can install a second copy of windows along side your current failed one, to allow you to back up data. If not, your data can still probably be save but it can be much more complex.

If your system gives 'Non-system disk' or 'Not a systems disk' error or another error with a similar wording, it is likely one of 3 things has happened:
a) in the BIOS (the most basic level of control on your computer) is looking on the wrong disk or drive. Normally you will be asked to press a certain key to 'enter setup' almost immediately after switching the machine on. After this each computer differs, and the range is too wide to describe, though with extra information, more instruction can be given.
b) the installation of Windows has been removed/deleted from your drive, possibly with all your data, either accidentally or by a virus. If your disk has been totally wiped, data recovery software which does not write to the disk can be used, but often requires the hard disk be placed in another computer for this. Then reinstall windows and copy the data back onto the drive. OR install windows straight off and risk losing your data.
c)your hard disk has a lose connection. Open up the computer and check all the connections. If you start the windows install and it says it can't find the hard disk, this may well be the problem!

If nothing comes up on the screen at all, there is a fault with one of the pieces of hardware. If the fans in the machine do not turn, the power supply could well have failed, though there are other reasons for this. If this is not the problem (determined by changing the internal power supply for a known to be working one, there are many instructions for this elsewhere on the web) then check that everything is properly connected and is firmly pushed into it's slots. If it still doesn't work then try replacing each part with a known to be working one until it does, or test the parts in another computer to prove they work! This can take and long time, and needs spares of all the parts in the computer.

grantpe, October 2007