Laptop strangeness

Hi all.
Acer Aspire 5738Z running Vista home.
Suddenly some of the keys have stopped working.
I have
1,3,-,q,w,e,r,t,y,u,p,[,],Enter,Caps Lock,a,s,d,f,g,h,j,k,Shift,\,z,x,c,v,b,n,m,,,.,/,shift,ctrl,alt,space,altgr,ctrl,arrowkeys.
All the others wont work.
Another strange thing is I can't access my account. My password starts with m, the m is working yet when I type the m in the password box it tells me straight away that my password or user name is invalid??
I have to use the guest account to get in.
I've tried using a USB keyboard and I get the same thing when trying to access my account but when I use the guest account all the keys on the USB keyboard work.
Any clues?
Cheers.

 

Thanks for the reply David.
Can't do safe mode as F8 isn't working either and the USB keyboard doesn't come into play until windows boots.
Further strangeness has happened.
The touch pad stopped working.
Then it allowed me to type my password into my account using the USB keyboard??
I rebooted, the touch pad started again but it wouldn't let me type my password in??
What the heck?

One other thing, it is only the letter m that prompts the laptop to say 'the user name or password is wrong' no other letters, working ones or not, will type into the password field?

 

Looks like I'm going to have to do a re install.
I've tried the malware clearance route but I have to keep rebooting after installing stuff which means I'm locked out again and I can't install stuff from the guest account as it hasn't got administrative rights!
It's madness.

 

Well, spent an age running malware tests.
Still the same so I decided to install windows 7.
Very glitchy and after researching I found many others had had similar problems.
The main one was a command prompt (X: blah blah blah) that just stayed on the screen.
If I shut it, the laptop rebooted and returned to the same place.
I had to mess about taking the disc out and in until it eventually moved on.
Anyway, after install I still had the same problem so I tried a different keyboard from my daughters laptop and it worked fine.
After all that all I needed was a new keyboard.
Aaaaaargh!!