Windows won't boot and more

I installed windows over a week ago, and it was working well. I had few more programs to install and did that on Sat. After install I rebooted and at startup, the startup repair began, but could not repair the problem. I tried a system recovery and that did not work. After more checking and trying many things including putting in the windows cd and doing a computer repair, all of which didn't work, I realized that somehow my drive letters had changed. I unplugged all the drives including the DVD ones and those that weren't turned on and still the same problem. I went to the command prompt and checked the drives with the new letters and all directories and files are there. I have a 1TB Hard Drive that I partioned and originally the C: was the OS, and J: the other partition for my files. I assigned the letter J to it. Now D: is the OS, and E: is the partition for the files. C: is the reserved system. When it first ran the startup repair and I sent the information to microsoft as an options the details showed a corrupt file D:\windows\systemwow64\drivers\pxhelp20.sys and error code= 0x2. I believe this could have been from some installs I had just done; Roxio Easy Media Creator 9 repair, or Sony Picture Utility for my Sony Handycam HDR-CX7.I had also installed Video Studio 11.5. I would really like to be able to get my system going again without a complete reinstall (It has taken me a week to get it all going!) I have read somewhere about renaming the pxhelp.sys file to pxhelp.sys.bak.

Here are the session details from Startup Repair:

System Disk=\device\hardisk 0
Windows directory= D:\Windows
Autochk Run=0
Number of root causes=1
All other checks were:
Result: completed successfully error code=0x0

I can provided more information if I need on my computer, just not at it right now and don't know it off the top of my head. Am running Windows 7 Home Premium. I have 2 DVD drives, a Lite On and an LG. Could it also involve a driver for one of them? The LG seemed to hang a little on the last installs of software. Also do a dare boot up from another drive that has my old XP still on it and get my user files off the OS partition so I don't have to recreate those from scratch?

I have run it 20 times! What is my next step?
Right now I would like to know opinions on if it is safe to plug in my old hard drive with XP and then look at the drives that 7 is on and check to see if my files are ok on the partition. I wish I could do an repair install over the first one to keep all my files and programs like they were. I guess that is not a option in windows 7, either a repair that doesn't work, or a clean install and reformatting the OS hard drive partition.

Unfortunately trying to boot from my old hard drive didn't work. Windows XP just kept restarting and bringing up the screen of which mode I wanted to boot into, tried them all and after the windows xp screen, the computer would just restart. I have checked the drive on another computer and it seems to be fine.

No, it is from the same machine. My old hard drive was a 250 GB with XP on it. I put in a new 1 TB hard drive. Partitioned it. Put windows 7 on it. Enclosed my old hard drive in a rosewill external enclosure. Also had another internal drive in the machine that had "My Documents" on it. Transferred all my files over the the partition that Windows 7 is not on. Installed several programs and all was working fine for 3-4 days. Installed new software and suddently windows won't boot up or do a repair. Remember, my drive letters were also changed somehow. I had spent alot of time transferring over my Firefox, Thunderbird, Picasa albums etc profiles, databases that are on the operating system partition with the programs and would really like to not have to do them all again. So I plug in the 250 GB drive with xp on it that used to be in the same machine and it won't boot up, just keeps restarting. I checked to make sure all cables, memory, cpu, etc were secure and haven't come loose. Any ideas?

Oh yea one more thing to mention, I hadn't installed any new hardware on the machine, just reinstalls of all hardware that was being used before. In bios setup on the main screen, my old hardrive doesn't show as either a primary or slave ide. Should it? also, both hard drives I am using are sata. One DVD drive is IDE and the other is SATA.