Hi gang You guys seem to know a lot about these things so I hope someone answers!
I had a hard disk fail on me (primary hdd error) and i connected it to my other working computer to see if there was life in it. I was able to read files on the HDD and stuff but it turned out later that it was defect anyway and that I couldn't reinstall windows on it or install much or anything. Was impossible.

Anyway the day after i disconnected that HDD the computer froze on the desktop screen completely and i resetted computer only to find cmos checksum error and floppy disk error message (which would mean failure to read my old HDDs i guess rather than a floppy disk). Actually before that the monitor would often give me "no signal" error or something of that sort when i would start up, and the frequency of that happening has been getting higher and higher until now it won't even show anything, ever.

The times it did get signal there were those checksum error messages on startup. Pressing F1 to continue resulted in a blue screen and an auto restart. So i went into bios settings and changed things but to my surprise the settings did not save any more no matter what.

So did the hard disk somehow destroy my motherboard? And will it do the same to any other computer I connect it to? Fixed up the original pc by getting a completely new hard disk and installing everything from scratch, but I'm afraid of connecting this "broken" one to the computer to transfer my files in fear of it killing my system the same way.

could it be something completely different like power supply malfunction?

Hello and welcome to PC Help Forum.

How old is this computer?

This could be as simple as needing a new BIOS battery or yes a failing power supply.

Settings may not of saved due to failed battery.Now these batterys come in diffrent thickness so you would have to write down the codes written on it or take battery to a local electrical shop to buy correct one.

I know in the UK they are around £2 so they are not expencive.

Hey stillalive, welcome to PCHF.

Well your half way there, it is the motherboard, but not in the way you might think. This is actually a common problem, and a result of a dead CMOS battery. In order to resolve your Checksum error, you'll need to replace this battery. The battery is normally a CR2032, which can be found in many hardware stores, but you can also buy one from: Stopwatches USA | CR-2032 Lithium Battery

Here is the instructions on how to replace: Replacing the Motherboard Battery | Hardware Secrets

The loss of a motherboard battery, even if the votage is low, can sometimes cause some strange problems. Sometimes it just means not saving your CMOS settings, date and time. Some other PC's can become completely unresponsive without it's battery (something to do with motherboard bus timings, can't quite remember from my uni days).

EDIT: Soz JB, too fast for me

Wow you guys are fast. Thanks a lot. Gonna have a look at the battery tomorrow. Sleepy time for Norway (for me).

Your welcome stillalive.it does look like a battery issue.

MM you typed more info than me,