Hi everyone!
Hope someone can assist me here as im not the fittest with computer hardware to say it modestly

Yesterday i was told to clean our office pc from some dust.
And as i saw when opening it was really needed...
Firstly i shut it down, turned of the power button, switched of the cables and finally opened it up then.
The whole cleaning process outside on the veranda lasted like 15-20 mins at the most.
It was kinda cold in this weather with 0° C (32° F i think) but i cant do such a mess inside.
Used a vacuum cleaner, a brush for the tricky spots with some compressed-air spray.
So far so good.
When plugging it in again an hour later i got this error while booting:
Disk Boot Failure. Insert System Disk And Press EnterConsequently shut it down again and checked if all connections where correct and tried again.
It all looked fine to me, but the very same problem appeared with the next system start.
I had to leave to work for some hours afterwards and decided to let it be for the day, but i have the very same issue today.
There are no cds/usb sticks and such attached to the computer that may cause troubles, but it just wont boot any more no matter what.
Accordingly inserted the recovery cd and let it boot from cd instead, e.g. choosing repair option.
It wont continue the setup though as it cant find a hard drive any more...
Installing the operating system again didnt work either due to that.
Thus im pretty sure the error is caused by the hard drive as there were no problems at all before.
Dont know what to do any more and im kinda lost with the google search for the last hours.
Now i got the fear to have damaged it yesterday eventually and already got hell for it...
Can the temperatures or the compressed air have caused this maybe?
In case it really is broken, what possibilities do i have to recover data or see whats wrong.
Like recommendations for diagnosis/recovery tools and such.
Keep in mind that i cant boot on that computer and that i cant spend some hundred euros for an expert or a program.
We have back ups of most data as its very important content of the store and all,
but the last complete back up file is from Jan 1 this year so that ~ 5 weeks are lost.
Its just the worst timing for something like this to happen im stressed out anyway.
Will be hell to go through all the paperwork again to catch this up on top of my regular jobs and exams...

System: Medion MD 8383 with Windows XP
( some parts changed in the meantime though, have to check which excactly. )
Harddrive: Western Digital WD2500JD (S-ATA 150/7200 )
Let me know if anything else is needed.
I will have to check on the internet or the manual then since i cant boot the computer any more.
Screen of the error message:

Thanks in advance for the help
