Auto Scan Disk

I am using a Dell Laptop, Insiron 8100, P-III, 1.2 Mhz, 256 meg, XP Home. Last Nov I replaced the hard drive. There where not any instructions as how to install the hard drive. It did not boot up. So I installed XP and all the drivers after a format. A couple of months after that it started to auto scan the hard drive on startup. It does this about every other or third startup. I had some other issues of connecting to the local network and the Dell support thought the problem was a bad network card. I had the local tech get on the line with Dell. Dell insisted that it was a bad network card. It wasn't a bad card. We had some other problems with the network, mainly the hub and eventually that got fixed. I took my conputer to a local service shop. They stated that the computer was being iimproperly turned off and corrupting files. I indicated that there was on one way to turn off the computer, unless you held down the power button. Than they thought that it was corrupting files when the battery got low and shut down. I have since watched this religiously and it still keeps atuo scans disk on startup. What is causing this?