Our company is still supporting Windows XP. They are part of a Active Directory based domain. Until Feb 2016 they were all accessible via RDP from the few trusted Domain Admins. Now about 4 - 6 sites out of 300 of them are failing to logon. When you first reboot them they can be accessed. After about a day they can't. The following was done so far.
Monitored perfmon for memory leaks. Could find any. (Remember it is only a handful of sites)
Updated the DNS addresses (Company wide changes were not implemented on some PC's thanks to group policy updates being killed by Microsoft with he AD DS migration from Windows Server 2003 to 2012.
Removed NetBIOS and made sure SMB was used instead. (That helped all clients)
Verified all patches were up to date. (most were and the rest were immediately updated manaually)
Verified no viruses were in effect
New features were added over time and the page swap file was out of range. Fixed that and made it static on another drive. (All clients showed improvements).
Other minor fixes include defrag and cleanup.