Blue screen when trying to login, after deleting/merging partitions

Hi,
My hard drive contained two partitions, the first one was for data storage and the second one for Win 7.
Today I decided to merge those two partitions in order to have some more space for my programs. I realised this was not simple because of the position of the partitions (the one with the data was at the left of the one containing the OS). So, I booted from a partitioning tool CD, deleted the first partition and then merged the unallocated space with the second one. I restarted my PC and Windows booted up - everything seemed alright. I was thinking that I would need some fixmbr or something like that to make it boot correctly, but it maded to the users login screen without any problems. I logged in and waited to see. Windows seemed to stuck at "Prepairing your desktop" screen. It finally moved on after some minutes but it only came up with a blue screen (assuming it is the desktop) with only the mouse pointer on it. No start button, taskbar, desktop shortcuts or anything else is visible. From that moment I restarted many times and every time I was facing the same things.

I used Ctrl-Alt-Del and got to the task manager, I managed to open the cmd through File/New task but I couldn't open the chkdsk(asked me to open cmd in elevated mode). I managed to browse the disk through task manager by clicking File, New task and then Browse and I found out that Windows partition letter changed from C to D. D: was actually the letter of the first partition I deleted.

So here I am now with a mess and I don't know what to do. I thought to change the drive letter through registry but I don't want to make things worse.

I really apologise for the long post and for my english, too.

Take a look here so we can help you :)
Blue Screen of Death (BSOD) Posting Instructions

this might be complicated

- try to restart, hit F8 until you stumbled on Advanced Startup
select Last Known Good Configuration

   Tip

from Task Manager, run cmd so it will open up elevated command. from there, you can run the chkdsk /r /f command

ok then try to run cmd then chkdsk from Task Manager