Operating temperature ranges vary somewhat by processor...but my guess is that anything up to 65 Celsius may be a bit high but not do any damage.
If this is a new system and the temps are high, it's not likely that dust/dirt is a factor...but the heatsink/fan may not be properly attached (assuming that it's custom-built). If it's a boxmaker (Dell, HP, etc.) system, then that is not a likely scenario.
What temperatures are you concerned about...what is reflected for CPU temperature in the BIOS?
As for shutdown problems, take a look at
Troubleshoot XP Shutdown Problems (MS) - http://support.microsoft.com/?kbid=308029
AND Troubleshooting Windows Shutdown Problems - http://www.windowsnetworking.com/articles_...s-Shutdown.html