Have an Radeon HD 7700 running under Windows 10 1903. Had two 27" LG IPS full HD monitors, running in extended mode. Worked find for the last 3 years. Replaced the two LG monitors with two 27" Dell monitors. computer boots up with two monitors, but after a minute one monitor goes black (sleep mode) and windows reports only one monitor. Change back to extended mode, which only last for 10 seconds. When I reconnect the two LG monitors, they both work as expected. What can be causing this?