It could be several things that have created this situation.
To take the safety first and hopefully quickest approach I suggest.
Connect the Hard Drive of your PC to another working system that has a good
Anti VFirus application. You may not need to remove it from the case, but
just connect it into the second IDE slot on the other PCs Mobo.
Boot up the other PC and perform a full virus scan on your hard drive. This
method ensures that nothing gets 'launched' during the windows startup and
that you hard drive is viewed only as a 'data' source.
If any viruses etc are identified, delete them and ensure that the recycle
bin is emptied and that the drive is clean of nasties.
If no viruses are detected then perform a scan disck to make sure that the
disk drive isn't faulty in itself. If any errors are found, then consider
that you may need to replace this ASAP.
You should then attempt to startup your PC. Should you receive any messages
about Windows not starting due to missing or corrupt files, shut down, insert
the Windows Installation CD and perform a repair Installation of XP. - see
below for step by step, how to.
If Windows restarts, then check out your Anti Virus apps, update or replace
with a good one and also get hold of a decent spyware detection and removal
app such as Spybot Search and Destroy. The name of the game is get protected
and stay protected.
Delete all the virus, worm, spyware etc nasties from your Hard Drive and
Windows Registry. It also serves to speed up the PC, keep your data safe,
keep your confidential details safe and protect from future infection or
attack.
Perform a Repair Install by following the step by step below.
Insert the XP installation CD and boot off the CD.
When you see the "Welcome To Setup" screen, you will see the options below
This portion of the Setup program prepares Microsoft
Windows XP to run on your computer:
To setup Windows XP now, press ENTER.
To repair a Windows XP installation using Recovery Console, press R.
To quit Setup without installing Windows XP, press F3.
Press Enter to start the Windows Setup.
Accept the License Agreement and Windows will search for existing Windows
installations.
Select the XP installation you want to repair from the list and press R to
start the repair.
Setup will copy the necessary files to the hard drive and reboot. Do not
press any key to boot from CD when the message appears. Setup will continue
as if it were doing a clean install, but your applications and settings will
remain intact.
Do not immediately activate over the internet when asked, enable the XP
firewall before connecting to the internet.
You can activate after the firewall is enabled. Control Panel - Network
Connections. Right click the connection you use, Properties, and there is a
check box on the advanced page.
Reapply updates or service packs applied since initial Windows XP
installation, you only need SP2 and subsequent updates, so don't do SP1 and
then SP2.
