"invalid system disk..." wut do i do?

Maybe, maybe not. Can you boot from a boot disk and access the drive? If so, then you can probably salvage the drive. If you don't have a boot disk go to bootdisk.com and download one for the os you are using. Boot from the boot disk. Since the message you are getting says the system cannot find the boot record let's attempt to repair that first. From your boot disk type "fdisk /mbr" (no quotes). That will attempt a repair on the mbr. Remove the boot disk and try to boot normally.

The bigger question is what made this happen. If he uses thepc on the internet then check for viruses and malware. Make sure you are scanning using the latest definitions. You can get a free anti-virus app at www.grisoft.com (AVG 7 free). You can get free adware/malware scanners at:

www.lavasoftusa.com/software/adaware/
and
www.safer-networking.org/en/index.html

(AdAware SE and Spybot Search & Destroy) respectively. They are all verygood products.

Post back with any further problems.

Cheers.

RW

Try out the method given in first answer
OR if nothing of this works then
boot up with any bootable cd of windows 98 or 2000 and reinstall your OS

First - make sure there's not ALREADY a floppy or a bootable CD (though I've RARELY had probs with CDs) in the drive, THEN follow the above instructions.

Sometimes the simplest answer is the correct one.

The message you describe is pretty normal when something has gone wrong with your boot signature.
Hence invalid system disk.

There are a few things you can do depending on the OS involved..

If your on Windows 2000 or XP with NTFS then booting to a Win98 disk will do you no good, as Fat (Win98) can't see NTFS formatted partitions.

If the OS is windows 98 then boot to the start up disk and run this command:

FDISK /FIXMBR

This can repair a damaged Master Boot Record (sometimes)

Good Luck..