There may not be enough hard disk space and low memory could be an issue. That laptop is incredibly old. Be sure that you backup your data because that Inspiron can fail at any minute.
If you really want to continue using it, then I would recommend moving (not copying) a lot of data to an external hard drive. Then run disk cleanup and disk defrag and restart. You may notice some improvement.
Honestly, it is 2007 and that laptop is oooollllldd. So old that it maxes out at 144MB and the memory that computers should come with nowadays is at least 1GB.
Rich Urban
August 2007