pc boots up to dos and says operating system not found, you hit enter or esc and it just repeats forever, so i reboot and same thing comes up "operating system not found", i cleaned the tower out of all dust inside and on the processor fan and fins, at this point I was trying anything and was actually going to part out my pc and trash the thing, I took it back and plugged in all the cables and rebooted it and still "operating system not found", I turned it off with the power button again and when it rebooted, scan disk popped up and I let it run, Now the pc works just fine, after scan disk, i ran defrag, and cleaned up temp. files, temp. folder and it's still working..before all this no operating system not found happened, I kept seeing a blue screen with the error message: "can't write to drive C",it would be up in the morning when i woke up,it might of said can't read drive C...NOW....after all that my question is: Whats going on?? Do I need to get it fixed before it crashes for good? or is it time to buy a new one??

Likely your hard drive is on it's way out. Back up all your important documents now while it's playing nicely and expect it to fail soon. I've seen this loads of times before and every time, the hard drive has gone bye bye.

Another reason for operating system not found is, the fast shutdown is enabled. If using Windows 2000 this run command will not work. Go to start run fill in "msconfig" (without the quotes) Click on the advanced tab check Disable Fast shutdown. Fast shutdown may skip the save you're settings that you see in Windows 2000 and XP but you don't see it in win 98se.