Noted in the Cnet Laptop Troubleshooting forum, here's the quick version.
Power off, remove the AC, then the battery then press and hold the power button for 60 seconds. Release, then slip in the battery, apply AC and try again.
As to the HDD contents, if you value what's on that drive you will NEVER let it near a repair center. The odds some tech will load an OS over the top must be about 100% these days.
If you want to back off or copy those files out I carry this cable with me when my friends have such trouble -> http://www.geeks.com/details.asp?invtid=2020
Once your files are safe you can proceed with repairs with less worry.
My dell inspiron 1720 screen doesnt show anything after it froze and shutdown after pressing ctrl + alt + del. Also, does fixing/replacing the motherboard affect the HDD at all?