Computer systems in the Welsh health service are "outdated" and failures are having a "negative impact" on patients, according to a new report.
An Assembly inquiry questioned the "competence, capability and capacity" of the body that looks after IT, the NHS Wales Informatics Service (NWIS).
There were 21 systems outages in the first half of this year, according to the public accounts committee.
The NWIS and Welsh Government said they would review the findings in detail.
Committee chairman Nick Ramsay said the cross-party report had uncovered a "raft of problems" in the dysfunctional system.
"As we begin scrutinising one area, we find that other, equally serious questions arise elsewhere," the report said.
"As a consequence, we are anxious that our scrutiny has merely scratched the surface of NWIS' problems."
NWIS was established in 2010 to deliver technology and digital services for patient care in Wales.
Establishing electronic patient records in Wales was one of its main projects.
But the report said there were "too many cases (where) the NHS relies on outdated, paper-based records" when electronic records could lead to better patient care.
The committee said they were "particularly concerned" to hear about the impact of outages on patient experience and staff morale at Cardiff's Velindre Hospital, although witnesses assured the committee no patients had come to harm during the IT failures.
The cancer IT system, CaNISC, was highlighted as a particular problem, with the report stating committee members were "alarmed" by evidence Microsoft stopped providing support for the system in 2014 and it posed a cyber security risk.
Richard Pugh, head of services at cancer charity Macmillan in Wales, said: "Continuing with the current 'patch-and-mend' approach on an obsolete IT system will not only heap additional pressure on our hard-working cancer care workforce, it runs the risk of putting cancer patients in Wales at risk and creating unnecessary stress for those going through treatment."
However, AMs acknowledged "funding is stretched", with NWIS trying to keep its existing system going while under pressure to deliver new ones.
The committee's inquiry followed a report by the Auditor General for Wales, published in January, which concluded that plans to digitise patients' NHS records in Wales face significant delays.
Mr Ramsay added: "Our inquiry has raised serious question marks about the competence, capability and capacity across the health system to deliver a digital transformation in Welsh healthcare.
"We trust our inquiry and this report will be a wake-up call to all those involved in harnessing the power of digital innovation to improve healthcare in Wales. We believe it's time for a reboot."
Recommendations include a call for a review of senior leadership capacity within both NWIS and the wider NHS digital team.
GPs said the report had raised some "alarming findings" and data outages were becoming "all too common".
Dr Peter Saul, of the Royal College of GPs in Wales, said: "Today, IT systems are as critical to clinicians as stethoscopes and scanners. Data outages can be extraordinarily disruptive for practices and for patients.
"They affect appointments, prescriptions and the nuts and bolts of a functioning practice and can take hours to recover from."
The NWIS welcomed the report and said it had been "pleased to share insight into the specification, planning, delivery and management of national digital health and care services for Wales".
The Welsh Government said it would provide a considered response in due course.